Display apparatus and liquid crystal display device

ABSTRACT

A display apparatus and a liquid crystal display device are provided. The display apparatus comprises a display device for displaying an image and a diffractive optical element. The diffractive optical element comprises pixel unit regions. Each of the pixel unit regions has a long pixel side and a short pixel side adjacent to each other. The diffractive optical element is disposed on a light emitting side of the display device and comprises first grating regions and second grating regions. The first grating regions have a first diffraction grating. The second grating regions have a second diffraction grating. An azimuth angle of the first diffraction grating is different from an azimuth angle of the second diffraction grating.

This application claims the benefits of Taiwan application Serial No.100111497, filed Mar. 31, 2011, and 101108364, filed Mar. 12, 2012, thesubject matters of which are incorporated herein by reference

BACKGROUND

1. Technical Field

The disclosure relates in general to a display apparatus and moreparticularly to a display apparatus having a diffractive opticalelement.

2. Description of the Related Art

Currently, an image display device mainly comprises a liquid crystaldisplay device, a plasma display device, an OLED display device and anelectronic paper display device, etc. The liquid crystal display deviceis a non-self-luminous display device, and thus usually needs abacklight source for generating light that entering the liquid crystaldisplay panel with a uniform plane profile through an optical film suchas a diffusion film, a brightener film, etc, for displaying an image.

J.P. patent application number 2003-302954, entitled “SPATIAL OPTICALMODULATOR, AND PROJECTOR”, has disclosed a projector having a projectionimage of high contrast, at low cost and with a simple construction. Anspatial optical modulator having a pair of counter substrate and a TFTsubstrate and a liquid crystal interposed between the counter substrateand the TFT substrate and modulating incident light from the countersubstrate side according to an image signal to emit the modulated lightfrom the TFT substrate side has a wedge prism deflecting incident lightto the light emission side of the TFT substrate.

EP. patent publication number 0567995A1, entitled “Image displayapparatus”, has disclosed an image display apparatus includes an imagedisplay device such as, a liquid crystal display panel having aplurality of dot-shaped picture elements arranged in a two-dimensionalpattern, and a diffraction grating disposed on an optical path throughwhich imagewise rays of light emerging from the device travel.

U.S. Pat. No. 6,483,612, entitled “Projection screen apparatus includingholographic optical element”, has disclosed a screen apparatus includesa holographic optical element and a diffuser. In operation, theholographic optical element receives image light from an image engine orprojector and redirects the image light to the diffuser for scattering.The holographic optical element can be designed to substantiallycollimate, converge, or diverge the image light.

A twisted nematic (TN) or a super twisted nematic (STN) liquid crystaldisplay device are types of the display devices usually used. Althoughthis kind of the liquid crystal display device has advantage in price,the viewing angle of which is smaller than that of a ordinary wideviewing angle liquid crystal display device, such as a multi-domainvertical alignment (MVA) liquid crystal display device, an in-planeswitching (IPS) liquid crystal display device, a fringe field switching(FFS) liquid crystal display device, etc.

The viewing angle means an angle range in which the display device candisplay an image quality of which is in a standard range. For example,for a general desktop liquid crystal display device, the main viewingangle is a front view. Therefore, for designers, the display device isdesigned according to the front view mainly since the optical effectwould be affect due to the arrangement of the liquid crystal molecule.Therefore, an observer would find images of different colors andbrightness with different oblique s to the liquid crystal displaydevice. At the same time, the image difference increases as the viewingangle increases. Among the liquid crystal display devices usually used,the TN liquid crystal display device has the worst condition. For a TNliquid crystal display device without using any compensating element forviewing angle, usually, an image observed from the side viewing angle ofthe liquid crystal display device has problems such as serious contrastdecreasing (to lower than 10), gray level reversion degrees, etc.

Therefore, a display apparatus for improving image quality problems suchas contrast, gray level reversion, etc is need.

SUMMARY

A display apparatus is provided. The display apparatus comprises aliquid crystal display, a first polarizer, a second polarizer and adiffractive optical element. The liquid crystal display device comprisesa backlight module and a liquid crystal panel. The liquid crystal panelcomprises a first substrate, a second substrate and a liquid crystallayer. The liquid crystal layer is disposed between the first substrateand the second substrate. The first polarizer is disposed on the firstsubstrate. The second polarizer is disposed between the second substrateand the backlight module. Polarizing directions of the first polarizerand the second polarizer have different azimuth angles. The diffractiveoptical element is disposed on a light emitting side of the firstpolarizer and has a first diffraction grating and a second diffractiongrating. Grating directions of the first diffraction grating and thesecond diffraction grating have different azimuth angles.

A display apparatus is provided. The display apparatus comprises aliquid crystal display device for displaying an image and a diffractiveoptical element. The liquid crystal display device comprises a backlightmodule and a liquid crystal panel. The liquid crystal panel is disposedon the backlight module and comprises a first substrate, a firstalignment film, a second substrate, a second alignment film, and aliquid crystal layer. The first alignment film is disposed on the firstsubstrate. The second alignment film is disposed on the secondsubstrate. Aligning directions of the first alignment film and thesecond alignment film have different azimuth angles. The liquid crystallayer is disposed between the first alignment film and the secondalignment film. The diffractive optical element is disposed on a lightemitting side of the liquid crystal display device and comprises a firstdiffraction grating and a second diffraction grating. An azimuth angleof a grating direction of the first diffraction grating is differentfrom an azimuth angle of a grating direction of the second diffractiongrating.

A liquid crystal display device for displaying an image is provided. Theliquid crystal display device comprises a liquid crystal panel and adiffractive optical element. The liquid crystal panel comprises a firstsubstrate, a second substrate and a liquid crystal layer. The liquidcrystal layer is disposed between the first substrate and the secondsubstrate. The liquid crystal layer comprises liquid crystal molecules.At least one of the liquid crystal molecules adjacent to the firstsubstrate has a first liquid crystal tilt direction. At least one of theliquid crystal molecules adjacent to the second substrate has a secondliquid crystal tilt direction. An azimuth angle of the first liquidcrystal tilt direction is different from an azimuth angle of the secondliquid crystal tilt direction. The diffractive optical element isdisposed on a light emitting side of the liquid crystal panel andcomprises a first diffraction grating and a second diffraction grating.An azimuth angle of a grating direction of the first diffraction gratingis different from an azimuth angle of a grating direction of the seconddiffraction grating.

A display apparatus is provided. The display apparatus comprises adisplay device for displaying an image and a diffractive opticalelement. The diffractive optical element comprises pixel unit regions.Each of the pixel unit regions has a long pixel side and a short pixelside adjacent to each other. The diffractive optical element is disposedon a light emitting side of the display device and comprises firstgrating regions and second grating regions. The first grating regionshave a first diffraction grating. The second grating regions have asecond diffraction grating. An azimuth angle of the first diffractiongrating is different from an azimuth angle of the second diffractiongrating.

The above and other aspects of the disclosure will become betterunderstood with regard to the following detailed description of thenon-limiting embodiment(s). The following description is made withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a three dimensional diagram of the display apparatusaccording to one embodiment of the present invention.

FIGS. 2-11 and 20-32 illustrate the diffractive optical elements inembodiments.

FIGS. 12-19 illustrate the grating regions of the diffractive opticalelements in embodiments.

FIG. 33 illustrates a cross-section view of the display apparatus in oneembodiment.

FIG. 34 illustrates a three dimensional diagram of the alignment filmand the liquid crystal layer of the display device.

FIG. 35 illustrates the liquid crystal tilt azimuth angle of the liquidcrystal molecule of the liquid crystal layer.

FIGS. 36-41 illustrate relations between the diffractive optical elementand the polarizing direction of the polarizer.

FIG. 42 illustrates the influence of the diffractive optical elementhaving the diffraction gratings of two kinds of the azimuth angles tothe contrast.

FIG. 43 illustrates gamma curves of the display apparatus without usingthe diffractive optical element (comparative example) from the frontview (zenith angle of 0 degree) and the side viewing angles (zenithangles of 45 degrees and 60 degrees).

FIG. 44 illustrates gamma curves of the display apparatus with using thediffractive optical element from the front view (zenith angle of 0degree) and the side viewing angles (zenith angles of 45 degrees and 60degrees).

FIG. 45 illustrates the influence of the diffractive optical elementhaving the diffraction gratings of three kinds of the azimuth angles tothe contrast and the brightness white state.

FIG. 46 illustrates the influence of the diffractive optical elementhaving the diffraction gratings of three kinds of the azimuth angles tothe contrast and the brightness black state.

FIG. 47 illustrates gamma curves of the display apparatus without usingthe diffractive optical element (comparative example) from the frontview (zenith angle of 0 degree) and the side viewing angles (zenithangles of 45 degrees and 60 degrees).

FIG. 48 illustrates gamma curves of the display apparatus with using thediffractive optical element from the front view (zenith angle of 0degree) and the side viewing angles (zenith angles of 45 degrees and 60degrees).

FIGS. 49-51 illustrate the relations between the diffractive opticalelement and the pixel of the display device.

FIGS. 52-59 illustrate the arrangements of the grating region and thepixel unit region.

FIG. 60 illustrates the relation curves between the contrast and thebrightness in the white state of the display apparatus and the gapdistance between the grating regions of the diffractive optical element.

DETAILED DESCRIPTION

FIG. 1 illustrates a three dimensional diagram of a display apparatusaccording to one embodiment of the present invention. FIGS. 2-11 and20-32 illustrate diffractive optical elements in embodiments. FIGS.12-19 illustrate grating regions of the diffractive optical elements inembodiments. FIG. 33 illustrates a cross-section view of the displayapparatus in one embodiment. FIG. 34 illustrates a three dimensionaldiagram of an alignment film and a liquid crystal layer in the displaydevice. FIG. 35 illustrates a liquid crystal tilt azimuth angle of aliquid crystal molecule of the liquid crystal layer. FIGS. 36-41illustrate relations between the diffractive optical element and thepolarizing direction of the polarizer. FIG. 42 shows a relation betweena contrast of the display device and the diffractive optical elementhaving the diffraction grating having two kinds of azimuth angles. FIG.43 illustrates gamma curves of the display apparatus without using thediffractive optical element (comparative examples) from the front view(zenith angle: 0 degree) and the side viewing angle (zenith angle: 45degrees and 60 degrees). FIG. 44 illustrates gamma curves of the displayapparatus with using the diffractive optical element from the frontview(zenith angle: 0 degree) and from the side viewing angle (zenithangle: 45 degrees and 60 degrees). FIG. 45 shows a relation among thediffractive optical element having diffraction gratings of three kindsof azimuth angles, the contrast and the brightness in the white state ofthe display device. FIG. 46 shows a relation among the diffractiveoptical element having the diffraction gratings of three kinds of theazimuth angles, the contrast and the brightness in the black state ofthe display device. FIG. 47 illustrates gamma curves of the displayapparatus without using the diffractive optical element (comparativeexample) from the front view (zenith angle: 0 degree) and from the sideviewing angle (zenith angle: 45 degrees and 60 degrees). FIG. 48illustrates gamma curves of the display apparatus with using thediffractive optical element from the front view (zenith angle: 0 degree)and from the side viewing angle (zenith angle: 45 degrees and 60degrees). FIGS. 49-51 illustrate relations between the diffractiveoptical element and the pixel of the display device. FIGS. 52-59illustrate arrangements of the grating region and a pixel unit region.FIG. 60 illustrates a relation among the contrast, the brightness in thewhite state, and the gap distance between the grating regions of thediffractive optical element of the display apparatus.

Referring to FIG. 1, the diffractive optical element 2 is disposed on alight emitting side of the display device 10 for displaying an image.The display device 10 may be a liquid crystal display device, a plasmadisplay device, an OLED display device and an electronic paper displaydevice, or other kinds of the display device for displaying an image.The display device 10 may be incorporated with other elements, such as atouch element for forming a touch panel. The diffractive optical element2 may be used with other elements, such as an anti-reflection film or atouch panel, and disposed on a light emitting side of the display device10 for displaying an image. The liquid crystal display device may be avertical aligned/multi-domain vertical aligned liquid crystal displaydevice, a twisted nematic (TN) liquid crystal display device, a supertwisted nematic (STN) liquid crystal display device, or an opticallycompensated bend (OCB) liquid crystal display device or color sequentialliquid crystal display (i.e. a liquid crystal display without colorfilter). The diffractive optical element 2 may be a film having agrating, such as a phase grating, for diffracting a light emitted fromthe display device 10. An observation angle to the liquid crystaldisplay device is presented by a zenith angle θ and an azimuth angle ψin spherical coordinate. The azimuth angle ψ indicates an included angleon the X-Y plane from the X-axis. The zenith angle θ indicates anincluded angle from the Z-axis perpendicular to the X-Y plane. Thepositive included angle represents a counter-clockwise-directionincluded angle, and the negative included angle represents aclock-wise-direction included angle.

Referring to FIG. 2, in embodiments, the diffractive optical element 32comprises the grating region 43 and the grating region 53 separated fromeach other. An “ordinary region (or non-grating region)” besides thegrating region 43 and the grating region 53 of the diffractive opticalelement 32 is a region that generates a low-degree diffraction effect.In particular, the grating region 43 and the grating region 53 cangenerate a high-degree effect diffraction effect of a intensity ratio ofthe total zero order diffraction light (the light having an emittingdirection same with an incident direction) to the total non-zero orderdiffraction light (the light having an emitting direction different froman incident direction) lower than 100:1 to a light passing through thegrating region 43 and the grating region 53 with a specific direction.The “ordinary region (or non-grating region)” generates the low-degreeeffect diffraction effect of a intensity ratio of the total zero orderdiffraction light (the light having an emitting direction same with anincident direction) to the total non-zero order diffraction light (thelight having an emitting direction different from an incident direction)higher than 100:1 to a light passing through the “ordinary region (ornon-grating region)”, so as to increase penetration quantity of thelight. Alternatively, the “ordinary region (or non-grating region)passes through no light almost. That is, a light-opaque region can havethe similar effect with the “ordinary region (or non-grating region).The grating regions 43 and the grating regions 53 are arranged in rows.The grating regions 43 and the grating regions 53 arranged inalternation constitute columns. The grating region 43 and the gratingregion 53 respectively have the diffraction grating 44 and thediffraction grating 54. The diffraction grating 44 and the diffractiongrating 54 respectively have constant period and uniform directions(azimuth angles). The connecting lines of the wave crests (or wavetroughs) of the diffraction grating 44 having a substantially constantgap distance between the connecting lines. The connecting lines of thewave crests (or wave troughs) of the diffraction grating 54 having asubstantially constant gap distance between the connecting lines.

In embodiments, the direction of the diffraction grating is thedirection of the connecting line of the wave crests (or the wavetroughs) of the diffraction grating structure. In embodiments, thedirection of the diffraction grating of the grating region is indicatedby a solid line. An included angle between the direction of thediffraction grating and the X-axis is the azimuth angle τ of thediffraction grating. In one embodiment, the period of the diffractiongrating represents a gap distance between the wave crests (or a gapdistance between the wave troughs. For example, the period D1 of thediffraction grating 44 is 1 μm, indicating that the gap distance betweenthe wave crests of the diffraction grating structure of the gratingregion 43 is 1 μm. The period D2 of the diffraction grating 54 may be 1μm. The direction of the diffraction grating 44 is different from thedirection of the diffraction grating 54. The direction of thediffraction grating 44 may be perpendicular to the direction of thediffraction grating 54. In this case, for example, the azimuth angle τ1of the diffraction grating 44 is 90 degrees. The azimuth angle of thediffraction grating 54 is 0 degree. The grating region 43 and thegrating region 53 may have spherical shapes respectively having adiameter K1 and a diameter K2, such as 28 μm-29 μm. A refractive indexof a material of the diffraction grating may be about 1.49. A heightbetween the wave crest and the wave trough of the diffraction gratingstructure is about 0.4 μm. For example, the refractive index of thematerial, the gap distance between the wave crests, or the heightbetween the wave crest and the wave trough of the diffraction gratingstructure are designed properly, for generating a high-degree effectdiffraction effect of a intensity ratio of the total zero orderdiffraction light (the light having an emitting direction same with anincident direction) to the total non-zero order diffraction light (thelight having an emitting direction different from an incident directionby a deflection angle bigger than 15 degrees) lower than 100:1 to alight passing through the diffraction grating structure with a specificdirection. The non-grating region is designed properly for generatingthe low-degree effect diffraction effect of an intensity ratio of thetotal zero order diffraction light (the light having an emittingdirection same with an incident direction) to the total non-zero orderdiffraction light (the light having an emitting direction different froman incident direction by a deflection angle bigger than 15 degrees)higher than 100:1 to a light passing through the non-grating region. Thedesign method for the non-grating region is not described in detailherein.

In other embodiments, the single grating region may have diffractiongratings having the same azimuth angle and various period. For example,the single grating region has diffraction gratings having two kinds ofthe gap distances between connecting lines of wave crests (or wavetroughs), substantially 1 μm and 0.5 μm. An area of the grating regionmay occupy 17.5%˜94% of an area of the diffractive optical element.

Referring to FIG. 2, in a line constituted by the grating region 43 andthe grating region 53 arranged in alternation, the closest gap distancebetween the grating region 43 and the grating region 53 may be constantor varied according to actual demands. For example, the closest gapdistances S1, S2 of the grating regions 43 and the grating regions 53may be 1 μm-15 μm, such as 1 μm, 9 μm, or 15 μm both. In otherembodiments, the gap distance S1 is 9 μm, and the gap distance S2 is 15μm. In another embodiment, the closest gap distance between the gratingregion 43 and the grating region 53 may be 0 or negative that is thegrating region 43 and the grating region 53 have an overlapping areatherebetween.

Referring to FIG. 2, for example, in a line constituted by the gratingregions 43 or in a line constituted by the grating regions 53, theclosest gap distance between the grating regions 43 or the closest gapdistance between the grating regions 53 may be adjusted to be constantor varied according to actual demands. In one embodiment, the closestgap distance S4 between the grating regions 43 and the closest gapdistance S5 between the grating regions 53 are respectively 1 μm-15 μm,such as 1 μm and 13 μm. In another embodiment, the closest gap distanceS4 between the grating regions 43 and the closest gap distance S5between the grating regions 53 may be 0 or negative that is the gratingregion 43 and the grating region 53 have an overlapping areatherebetween.

In one embodiment, the azimuth angle the first kind of the diffractiongrating of the diffractive optical element is 0±60 degrees, that is theangle is in a range of bigger than and equal to −60 degrees, smallerthan and equal to +60 degrees, and equal to 0 degree, and the similarconcept is not described repeatedly hereafter. The azimuth angle thefirst kind of the diffraction grating of the diffractive optical elementis 0±20 degrees preferably. In addition, the azimuth angle the secondkind of the diffraction grating of the diffractive optical element is90±60 degrees, preferably 90±20 degrees. In another embodiment, theazimuth angle of the diffraction grating of the first kind is +45degrees, ±20 degrees, preferably ±45±10 degrees, and the azimuth angleof the diffraction grating of the second kind is 135±20 degrees,preferably 135±10 degrees. In yet another embodiment, the azimuth angleof the diffraction grating of the first kind is −45±20 degrees,preferably −45±10 degrees, and the azimuth angle of the diffractiongrating of the second kind is 45±20 degrees, preferably 45±10 degrees.An area of the grating region of the first kind may occupy 17.5%˜38.5%of an area of the diffractive optical element, and an area of thegrating region of the second kind may occupy 17.5%˜38.5% of the area ofthe diffractive optical element. The diffractive optical element 62 inFIG. 3 is different from the diffractive optical element 32 in FIG. 2 inthat the diffractive optical element 62 has a grating region 73 having adiffraction grating 74 of a constant azimuth angle.

The diffractive optical element 82 in FIG. 4 is different from thediffractive optical element 32 in FIG. 2 in that the diffractive opticalelement 82 comprises grating regions 93, 103 and 113 respectively havingdiffraction gratings 94, 104 and 114 of different azimuth angles. Forexample, the azimuth angle τ2 of the diffraction grating 94 is 135degrees, the azimuth angle of the diffraction grating 104 is 0 degree,and the azimuth angle τ3 of the diffraction grating 114 is 45 degrees.

In one embodiment, the azimuth angles of the diffraction gratings of thefirst kind, the second kind and the third kind of the diffractiveoptical element are respectively 90±15 degrees, 135±15 degrees and 45±15degrees.

In another embodiment, the azimuth angles of the diffraction gratings ofthe first kind, the second kind and the third kind are respectively15±10 degrees, 60±10 degrees and −30±10 degrees. In yet anotherembodiment, the azimuth angle of the diffraction grating of the firstkind is 0±40 degrees, preferably 0±20 degrees, the azimuth angle of thediffraction grating of the second kind is 45±40 degrees, preferably45±20 degrees, and the azimuth angle of the diffraction grating of thethird kind is 135±40 degrees, preferably 135±20 degrees. An area of thegrating region of the first kind may occupy 17.5%˜38.5% of an area ofthe diffractive optical element. An area of the grating region of thesecond kind may occupy 17.5%˜38.5% of an area of the diffractive opticalelement. In addition, an area of the grating region of the third kindmay occupy 17.5%˜38.5% of an area of the diffractive optical element.

The diffractive optical element 122 in FIG. 5 is different from thediffractive optical element 32 in FIG. 2 in that the grating regions 133and the grating regions 143 are respectively arranged in rows, and thegrating regions 133 and the grating regions 143 are arranged inalternation in rows vertically.

The diffractive optical element 142 in FIG. 6 is different from thediffractive optical element 132 in FIG. 5 in that a horizontal (Xdirection) period C1 between the grating regions 145 is different fromthe horizontal period C2 between the grating regions 146. In oneembodiment, the period C1 is 30 μm, and the period C2 is 48 μm. Inaddition, the vertical (Y direction) cycle space C3 between the gratingregion 145 and the grating region 146 is 41 μm. The cycle space alsomeans an appearing cycle between the grating regions respectively havingdifferent grating directions.

The diffractive optical element 152 in FIG. 7 is different from thediffractive optical element 32 in FIG. 2 in that all the grating regions163 and the grating regions 173 are arranged in alternation.

The diffractive optical element 182 in FIG. 8 is different from thediffractive optical element 32 in FIG. 2 in that the diffraction grating194 of the grating region 193 and the diffraction grating 204 of thegrating region 203 have azimuth angles other than 0 degree and 90degrees. For example, the azimuth angle τ4 of the diffraction grating194 is 45 degrees. The azimuth angle τ5 of the diffraction grating 204is 135 degrees.

The diffractive optical element 183 in FIG. 9 is different form thediffractive optical element 182 in FIG. 8 in that the horizontal (Xdirection) period C4 between the grating regions 185 is different fromthe horizontal period C5 between the grating regions 186. In oneembodiment, the period C4 is 30 μm, and the period C5 is 48 μm. Inaddition, the vertical (Y direction) cycle space C6 between the gratingregion 185 and the grating region 186 is 41 μm.

In one embodiment, the diffractive optical element may have gratingregions of more than three kinds of diffraction grating directions.

Referring to FIG. 10, for example, the diffractive optical element 202has the grating region 205, the grating region 206 and the gratingregion 207. The azimuth angle of the diffraction grating 208 of thegrating region 205 is 135 degrees. The azimuth angle of the diffractiongrating 209 of the grating region 206 is 0 degree. The azimuth angle ofthe diffraction grating 210 of the grating region 207 is 90 degrees. Inembodiments, the grating regions 205 having a higher amount (or density)are arranged into one row, and the grating regions 206 and the gratingregions 207 having a lower amount (or density) are arranged inalternation into another raw, so as to utilizing arrangement space ofthe diffractive optical element 202 properly. In a case of the TN panelusing the diffractive optical element 202, the grating region 205 ismainly used for compensating up and down gray level reversion direction,and the grating region 206 and the grating region 207 are mainly usedfor compensating 45 degrees and −45 degrees direction. That is, thediffractive optical element 202 is used by rotating 45 degrees (+45degrees) counterclockwise. In one embodiment, the horizontal (Xdirection) period C7 between the grating regions 205 is different fromthe horizontal (X direction) period C8 between the grating region 206and the grating region 207. For example, the period C7 is 36 μm, and theperiod C8 is 32 μm. In another embodiment, the vertical (Y) cycle spaceC9 between the grating region 205 and the grating region 207 (or thegrating region 206) is 36 μm.

Referring to FIG. 11, for example, the azimuth angle of the diffractiongrating 174 of the diffractive optical element 192 is 0 degree. Theazimuth angle τ6 of the diffraction grating 184 is 45 degrees. Theazimuth angle τ7 of the diffraction grating 214 is 90 degrees. Inaddition, the azimuth angle τ8 of the diffraction grating 234 is 135degrees. In another embodiment, in the diffractive optical elementhaving the diffraction gratings of more than three kinds of the azimuthangles, the grating regions having different azimuth angles may bearranged in alternation.

In one embodiment, the diffraction grating direction of the singlegrating region is not limited to only one direction. The single gratingregion may have the diffraction grating of various azimuth angles. Inaddition, the grating region is not limited to the spherical shape asshown in FIGS. 2-11. For example, in embodiments, the single gratingregion having four kinds of the diffraction grating directions maycomprise square shape (FIG. 12), rectangle shape (FIG. 13) or otherquadrilateral shapes. For example, the single grating region havingthree kinds of the diffraction grating directions may comprise regulartriangle shape (FIG. 14), isosceles triangle shape (FIG. 15),non-isosceles triangle shape (FIG. 16). For example, the single gratingregion having multiple kinds of the diffraction grating directions maycomprise regular pentagon shape (FIG. 17) or other regular pentagonshapes; or regular octagon shape (FIG. 18) or other octagon shapes; orspherical shape (FIG. 19) or other curved shapes; or other suitableshapes. In addition, the effect from the grating of polygon shape canalso be obtained a combination of the gratings of different directions,and therefore the present disclosure is not limited to the grating ofpolygon shape.

In some embodiments, the diffractive optical element 212 comprises thegrating region 223 as shown in FIG. 20. Referring to FIG. 20, in oneembodiment, the period T of the grating region 223 is 124 μm. A width Wof the grating region 223 is 116 μm-118 μm. The period N of thediffraction gratings 224 is 1 μm. The gap distance M between thediffraction gratings 224 is 6 μm-8 μm. In another embodiment, the gapdistance between the grating regions 223 may be 0 or negative. Thenegative gap distance means the adjacent grating regions 223 have anoverlapping region therebetween.

Referring to FIG. 21, the diffractive optical element 232 may alsocomprise the diffraction grating 244, the diffraction grating 254. Thediffractive optical element 232 may also be regarded as a result of thegrating region having the diffraction grating 244 and the grating regionhaving the diffraction grating 254 overlapped with each other. In oneembodiment, the diffractive optical element 262 comprises the gratingregion 273 and the grating region 283 as shown in FIG. 22.

Referring to FIG. 23, the diffractive optical element 263 comprises thegrating region 264 and the grating region 265. The azimuth angle of thediffraction grating 267 of the grating region 264 is 45 degrees. Theazimuth angles of the diffraction grating 268 and the diffractiongrating 269 of the grating region 265 are 90 degrees and 0 degree,respectively. In one embodiment, the width W1 of the grating region 264measured along the azimuth angle of 135 degrees and the width W2 of thegrating region 265 measured along the azimuth angle of 135 degrees are20 μm, respectively. The gap distances C10 or C11 of the grating region264 and the grating region 265 along the azimuth angle of 135 degreesare 60 μm.

Referring to FIG. 24, the diffractive optical element 271 comprises thegrating region 272 and the grating region 274. The azimuth angle of thediffraction grating 275 of the grating region 272 is 45 degrees. Theazimuth angle of the diffraction grating 276 of the grating region 274is 135 degrees. In one embodiment, the horizontal (X direction) width W3of the grating region 272 and the horizontal (X direction) width W4 ofthe grating region 274 are 20 μm, respectively. The horizontal (Xdirection) gap distance between the grating region 272 and the gratingregion 274 is 36 μm.

Referring to FIG. 25, the diffractive optical element 277 comprises thegrating region 278, the grating region 279 and the grating region 280.The azimuth angle of the diffraction grating 281 of the grating region278 is 90 degrees. The azimuth angle of the diffraction grating 282 ofthe grating region 279 is 45 degrees. The azimuth angle of thediffraction grating 284 of the grating region 280 is 135 degrees. In oneembodiment, the horizontal (X direction) width W5 of the grating region278, the horizontal (X direction) width W6 of the grating region 279 andthe horizontal (X direction) width W7 of the grating region 280 are all28 μm. The horizontal (X direction) cycle space C12 between the adjacentgrating region 278 and grating region 279 is 60 μm. The horizontal (Xdirection) cycle space C13 between the adjacent grating region 278 andgrating region 280 is 60 μm.

Referring to FIG. 26, in one embodiment, for example, the horizontal (Xdirection) width W8 of the grating region 286 is 22 μm. The horizontal(X direction) width W9 of the grating region 287 and the horizontal (Xdirection) width W11 of the grating region 289 are 18 μm, respectively.The horizontal (X direction) width W10 of the grating region 288 is 14μm. The closest distance S12 between the grating region 286 and thegrating region 287 is 25 μm. The closest distance S13 between thegrating region 286 and the grating region 289 is 15 μm. In otherembodiments, the element may be constituted by overlapping twodiffractive optical elements 277 as shown in FIG. 25.

Referring to FIG. 27, the diffractive optical element 290 comprises thegrating region 291, the grating region 293 and the grating region 294.In one embodiment, the horizontal (X direction) width W12 of the gratingregion 291, the horizontal (X direction) width W13 of the grating region293, and the horizontal (X direction) width W14 of the grating region294 are 28 μm, respectively. The closest distance S14 between theadjacent grating regions 291 is 5 μm.

The diffractive optical element 292 may also comprise the grating region303 and the grating region 313 as shown in FIG. 28.

The grating regions of the diffractive optical element are not limitedto order arrangement, and can be adjusted into disorder arrangementaccording to actual demands. Referring to FIG. 29, for example, thediffractive optical element 322 may also comprise the grating region333, the grating region 343, the grating region 353, the grating region363 and the grating region 373 disorderly.

In embodiments, the many diffractive optical elements can be overlappedfor using according to actual demands. The diffractive optical elementsof different levels may be arranged by overlapping the grating regionshaving the same pattern, i.e. the same shape or the same diffractiongrating, of different levels with each other, or by overlapping thegrating regions having different patterns, i.e. different shapes ordiffraction gratings of different characteristics. Referring to FIG. 2,for example, in a case of overlapping one diffractive optical element 32with another diffractive optical element 32, the grating region 53 ofthe one diffractive optical element 32 is overlapped with the gratingregion 43 of the another diffractive optical element 32, and the gratingregion 43 of the one diffractive optical element 32 is overlapped withthe grating region 53 of the another diffractive optical element 32. Forexample, after an laser light source is emitted to a single-layerdiffractive optical element 32 as shown in FIG. 2, diffraction lights oftwo directions such as 0/180 degrees or 90/270 degrees are formed.Conversely, after the laser light source is emitted to a stackedstructure constituted by multi-layer diffractive optical elements, notonly the transmission light having the diffraction directions as formedby the single-layer diffractive optical element, but also transmissionlights having other diffraction directions such as oblique directions.Cause of this is from the additional the cycle structure for the obliquedirection. In addition, it is presumed that diffraction light emittedfrom the grating region adjacent to a light source and generated from alight emitted into and the perpendicular to grating region adjacent tothe light source is further diffracted by the grating region away fromthe light source. Therefore, besides the diffraction lights of twodirections such as 0/180 degrees or 90/270 degrees are generated by thesingle-layer diffractive optical element, additional diffraction lightsof other oblique directions such as 45 degrees, 135 degrees, 225degrees, or 315 degrees or a bisector angle of the azimuth angles of twodiffraction gratings are formed.

In embodiments, the stacked structure constituted by the diffractiveoptical elements of various layers may be constituted by overlapping thegrating regions of the same pattern according to actual demands.Referring to FIG. 2, in one embodiment, for example, one diffractiveoptical element 32 is overlapped with another diffractive opticalelement 32. The grating region 43 of the one diffractive optical element32 is overlapped with the grating region 43 of the another diffractiveoptical element 32. The grating region 53 of the one diffractive opticalelement 32 is overlapped with the grating region 53 of the anotherdiffractive optical element 32. It can increase diffraction effect.

Referring to FIG. 30, the diffractive optical element 334 may beconstituted by overlapping two diffractive optical elements. Forexample, one of the two diffractive optical elements has the gratingregion 335A and the grating region 335B, and the other of the twodiffractive optical elements has the grating region 336. The azimuthangle of the diffraction grating 337A of the grating region 335A and thediffraction grating 337B of the grating region 335B are both 135degrees. The azimuth angle of the diffraction grating 338 of the gratingregion 336 is 45 degrees. The horizontal (X direction) period C14between the grating regions 335A of the first raw and the third raw is36 μm. The horizontal (X direction) period C15 between the gratingregions 336 of the second raw and the fourth raw is 41 μm. In addition,the horizontal (X direction) period C25 between the grating regions 335Bis 41 μm. The vertical (Y direction) period C26 between the gratingregions 335A is 72 μm. The vertical (Y direction) cycle space C16between the grating region 335A and the grating region 336 is 36 μm.

Referring to FIG. 31, the diffractive optical element 339 may beconstituted by overlapping two diffractive optical elements. Forexample, one of the two diffractive optical elements has the gratingregion 340A and the grating region 340B, and the other of the twodiffractive optical elements has the grating region 341. The azimuthangle of the diffraction grating 342A of the grating region 340A and thediffraction grating 342B of the grating region 340B are both 0 degree.The azimuth angle of the diffraction grating 334 of the grating region341 is 90 degrees. The horizontal (X direction) period C17 between thegrating regions 340A of the first raw and the third raw is 36 μm. Thehorizontal (X direction) period C18 between the grating regions 341 ofthe second raw and the fourth raw is 41 μm. In addition, the horizontal(X direction) period C27 between the grating regions 340B is 41 μm. Thevertical (Y direction) period C28 between the grating regions 340A is 72μm. The vertical (Y direction) cycle space C19 between the gratingregion 340A and the grating region 341 is 36 μm.

Referring to FIG. 32, the diffractive optical element 345 comprises thegrating region 346, the grating region 347 and the grating region 348.In one embodiment, the horizontal (X direction) period C20 between thegrating regions 346 is 26 μm. The horizontal (X direction) period C21between the grating regions 347 is 48 μm. The horizontal (X direction)period C22 between the grating regions 348 is 26 μm. The vertical (Ydirection) of the cycle space C23 between the grating region 346 and thegrating region 347 is 41 μm. The vertical (Y direction) of the cyclespace C24 between the grating region 347 and the grating region 348 is41 μm.

In embodiments, the diffractive optical element is adjusted according tocondition and effect for the display device.

Referring to FIG. 33, in embodiments, the display device 410 is a liquidcrystal display device. The display device 410 comprises a backlightmodule 411, a liquid crystal panel 427, the polarizer 415 and thepolarizer 425. The liquid crystal panel 427 is disposed on the backlightmodule 411. For example, the liquid crystal panel 427 comprises a thinfilm transistor substrate 416, a liquid crystal layer 418, a colorfilter substrate 421, the alignment film 417 and the alignment film 419.The alignment film 419 may be disposed on the color filter substrate421. The alignment film 417 may be disposed on the thin film transistorsubstrate 416. The liquid crystal layer 418 may be disposed between thealignment film 417 and the alignment film 419. The polarizer 415 may bedisposed between the thin film transistor substrate 416 and thebacklight module 411 (on the light entering side of the liquid crystalpanel 427). The polarizer 425 may be disposed on the color filtersubstrate 421 (the light emitting side of the liquid crystal panel 427.The diffractive optical element 402 may be disposed on the lightemitting side of the polarizer 425. The diffractive optical element 402is disposed by placing the wave crest structure facing the polarizer 425or opposite to the polarizer 425. The diffractive optical element 425may be used by stacking with other elements having different functions,such as an anti-reflection film, a scratch-resistant film, etc.

In some embodiments, the display device 410 is a twisted nematic (TN)liquid crystal display device. In this case, referring to FIG. 34, theazimuth angle of the aligning direction 426 of the alignment film 417 isarranged not parallel to the azimuth angle of the aligning direction 436of the alignment film 419. The liquid crystal molecules 428 in theliquid crystal layer 418 are aligned by the alignment film 417 and thealignment film 419, and thus the liquid crystal molecules 428 a (i.e.top layer liquid crystal molecule) adjacent to the alignment film 419(i.e. top layer alignment film adjacent to the color filter substrate421 in FIG. 33) and the liquid crystal molecule 428 b (i.e. bottom layerliquid crystal molecule) adjacent to the alignment film 417 (i.e. bottomlayer alignment film adjacent to the thin film transistor substrate 416in FIG. 33 are aligned into a twisted structure and to have pretiltangles. One end of the liquid crystal molecule having the pretilt angleaway from the alignment film is referred to as a head end, and the otherend of the liquid crystal molecule is referred to as a tail end. Forexample, the alignment film 419 is used for aligning the top layerliquid crystal molecules 428 a to have the pretilt angle. For example,the alignment film 417 is used for aligning the bottom layer liquidcrystal molecules 428 b to have the pretilt angle. The alignment film417 and the alignment film 419 are arranged to the aligning directionsof which not parallel to each other for aligning the liquid crystalmolecules 428 therebetween to twist continuously into a twistedstructure. In the twisted structure, the twist angle of the liquidcrystal molecules 428 may be defined as an angle twist continuously fromthe head end of the bottom layer liquid crystal molecule 428 b, throughthe middle layer liquid crystal molecule, to the tail end of the toplayer liquid crystal molecule 428 a.

Moreover, for conventional the twisted nematic (TN) liquid crystaldisplay device, an optical characteristic of a viewing angle, rangedfrom the head end of the bottom layer liquid crystal molecule 428 btwisted continuously, through the middle layer liquid crystal molecules,to the tail end of the liquid crystal molecules 428 a, is not good andthus is usually defined as a look-down angle direction for a viewer. Theabove region for poor viewing angle can also be defined as some viewingangle directions for a viewer.

The azimuth angle of the liquid crystal molecule tilted relative to thesubstrate is defined as the tilt azimuth angle. For example, as theliquid crystal molecule is aligned or driven to have a specific includedangle with the substrate, the tilted liquid crystal has the azimuthangle relative to the horizontal plane of the substrate. In other words,the included angle between the projection direction of the head end ofthe liquid crystal molecule on the horizontal plane of the substrate andthe X-axis of the substrate is defined as liquid crystal tilt azimuthangle. For the liquid crystal display device is a multi-domain verticalaligned liquid crystal display device, it can be understood that variousliquid crystal tilt azimuth angles can be generated at the same time.

In some embodiments, the diffractive optical element is designedaccording to the condition of the liquid crystal molecules 428 of thedisplay device 410 (FIG. 34). Referring to FIG. 35, for example, theliquid crystal molecules 428 a has the liquid crystal tilt azimuth angleQ1, such as 45 degrees. The liquid crystal molecule 428 b has the liquidcrystal tilt azimuth angle Q2, such as 315 degrees. In this case, thediffractive optical element having the diffraction gratings having theazimuth angles of 0 degree and 90 degrees may be used. In addition, thedensity (i.e. area percentage of grating occupying the diffractiveoptical element) of the diffraction grating having the grating directionhaving the azimuth angle of 0 degree is bigger than or equal to thedensity of the diffraction grating having the azimuth angle of 90degrees. For example, diffractive optical element 32 as shown in FIG. 2may be used. In other embodiments, the diffractive optical elementhaving diffraction gratings having azimuth angles of 0 degree, 45degrees and 135 degrees may be used. In addition, the density of thediffraction grating having the azimuth angle of 0 degree is bigger thanor equal to the density of the diffraction gratings having the azimuthangles of 45 degrees and 135 degrees, respectively. For example, thediffractive optical element 82 as shown in FIG. 4 may be used. In oneembodiment, the included angle between the grating direction of thefirst kind of the diffraction grating of the diffractive optical elementand the tilt direction of the top layer liquid crystal molecule is 90±10degrees or 0±10 degrees. The included angle between the gratingdirection of the second kind of the diffraction grating of thediffractive optical element and the tilt direction of the top layerliquid crystal molecule is 180±10 degrees or 90±10 degrees.

In one embodiment, as the included angle between the tilt directions ofthe top layer and the bottom layer liquid crystal molecules is 90degrees, the included angle from the grating direction of the first kindof the diffraction grating of the diffractive optical element to thetilt direction of the top layer liquid crystal molecule is 0±20 degrees,preferably 0±10 degrees, and the included angle from the gratingdirection of the second kind of the diffraction grating of thediffractive optical element to the tilt direction of the top layerliquid crystal molecule is −90±20 degrees, preferably −90±10 degrees. Inanother embodiment, as the included angle between the tilt directions ofthe top layer and the bottom layer liquid crystal molecules is 90degrees, the included angle from the grating direction of the first kindof the diffraction grating of the diffractive optical element to thetilt direction of the top layer liquid crystal molecule is 90±20degrees, preferably 90±10 degrees, and the included angle from thegrating direction of the second kind of the diffraction grating of thediffractive optical element to the tilt direction of the top layerliquid crystal molecule is 0±20 degrees, preferably 0±10 degrees. In yetanother embodiment, as the included angle between the tilt directions ofthe top layer and the bottom layer liquid crystal molecules is 90degrees, the included angle from the grating direction of the first kindof the diffraction grating of the diffractive optical element to thetilt direction of the top layer liquid crystal molecule is 45±60degrees, preferably 45±20 degrees and more preferably 45±10 degrees, andthe included angle from the grating direction of the second kind of thediffraction grating of the diffractive optical element to the tiltdirection of the top layer liquid crystal molecule is −45±60 degrees,preferably −45±20 degrees and more preferably −45±10 degrees.

In one embodiment, the included angle from the grating direction of thefirst kind of the diffraction grating of the diffractive optical elementto the tilt direction of the top layer liquid crystal molecule is 45±20degrees, preferably 45±10 degrees, the included angle from the gratingdirection of the second kind of the diffraction grating of thediffractive optical element to the tilt direction of the top layerliquid crystal molecule is 0±20 degrees, preferably 0±10 degrees, andthe included angle from the grating direction of the third kind of thediffraction grating of the diffractive optical element to the tiltdirection of the top layer liquid crystal molecule is 90±20 degrees,preferably 90±10 degrees. In another embodiment, as the included anglebetween the tilt directions of the top layer and the bottom layer liquidcrystal molecules is 90 degrees, the included angle from the gratingdirection of the first kind of the diffraction grating of thediffractive optical element to the tilt direction of the top layerliquid crystal molecule is −45±15 degrees, the included angle from thegrating direction of the second kind of the diffraction grating of thediffractive optical element to the tilt direction of the top layerliquid crystal molecule is 90±15 degrees, and the included angle fromthe grating direction of the third kind of the diffraction grating ofthe diffractive optical element to the tilt direction of the top layerliquid crystal molecule is 0±15 degrees. In one embodiment, as theincluded angle between the tilt directions of the top layer and thebottom layer liquid crystal molecules is 90 degrees, the included anglefrom the grating direction of the first kind of the diffraction gratingof the diffractive optical element to the tilt direction of the toplayer liquid crystal molecule is 30±10 degrees, the included angle fromthe grating direction of the second kind of the diffraction grating ofthe diffractive optical element to the tilt direction of the top layerliquid crystal molecule is −15±10 degrees, and the included angle fromthe grating direction of the third kind of the diffraction grating ofthe diffractive optical element to the tilt direction of the top layerliquid crystal molecule is 75±10 degrees. In one embodiment, as theincluded angle between the tilt directions of the top layer and thebottom layer liquid crystal molecules is 90 degrees, the included anglebetween from grating direction of the first kind of the diffractiongrating of the diffractive optical element to the tilt direction of thetop layer liquid crystal molecule is 45±20 degrees, the included anglefrom the grating direction of the second kind of the diffraction gratingof the diffractive optical element to the tilt direction of the toplayer liquid crystal molecule is 0±20 degrees, and the included anglefrom the grating direction of the third kind of the diffraction gratingof the diffractive optical element to the tilt direction of the toplayer liquid crystal molecule is 90±20 degrees.

In some embodiments, the diffractive optical element may be designedaccording to the alignment film 417, the alignment film 419 of thedisplay device 410 (FIG. 33). For example, in one embodiment, theazimuth angle of the aligning direction of the alignment film 419 is 45degrees, and the azimuth angle of the aligning direction of thealignment film 417 is −45 degrees. In this case, the diffractive opticalelement having the diffraction gratings having the grating directionshaving the azimuth angles of 0 degree and 90 degrees may be used. Inaddition, in some embodiments, the density of the diffraction gratinghaving the grating direction having the azimuth angle of 0 degree isbigger than or equal to the density of the diffraction grating havingthe grating direction having the azimuth angle of 90 degree. Forexample, the diffractive optical element 32 in FIG. 2 may be used. Inother embodiments, the diffractive optical element having thediffraction gratings having the grating directions having the azimuthangles of 0 degree, 45 degrees and 135 degrees may be used. In addition,the density of the diffraction grating having the grating directionhaving the azimuth angle of 0 degree is bigger than or equal to thedensities of the diffraction gratings having the grating directionshaving the azimuth angles of 45 degrees and 135 degrees, respectively.For example, the diffractive optical element 82 in FIG. 4 may be used.

In one embodiment, as the included angle between the aligning directionsof the upper alignment film and the lower alignment film is 90 degrees,the included angle from the grating direction of the first kind of thediffraction grating of the diffractive optical element to the aligningdirection of the top layer alignment film is 45±60 degrees, preferably45±20 degrees and more preferably 45±10 degrees, and the included anglefrom the grating direction of the second kind of the diffraction gratingof the diffractive optical element to the aligning direction of the toplayer alignment film is −45±60 degrees, preferably −45±20 degrees andmore preferably −45±10 degrees. In another embodiment, the includedangle from the grating direction of the first kind of the diffractiongrating of the diffractive optical element to the aligning direction ofthe top layer alignment film is 0±20 degrees, preferably 0±10 degrees,and the included angle from the grating direction of the second kind ofthe diffraction grating of the diffractive optical element to thealigning direction of the top layer alignment film is −90±20 degrees,preferably −90±10 degrees. In one embodiment, the included angle fromthe grating direction of the first kind of the diffraction grating ofthe diffractive optical element to the aligning direction of the toplayer alignment film is +90±20 degrees, preferably +90±10 degrees, andthe included angle from the grating direction of the second kind of thediffraction grating of the diffractive optical element to the aligningdirection of the top layer alignment film is 0±20 degrees, preferably0±10 degrees.

In one embodiment, as the included angle between the tilt directions ofthe top layer and the bottom layer liquid crystal molecules is 90degrees, the included angle from the grating direction of the first kindof the diffraction grating of the diffractive optical element to thealigning direction of the top layer alignment film is −45±15 degrees,the included angle from the grating direction of the second kind of thediffraction grating of the diffractive optical element to the aligningdirection of the top layer alignment film is 90±15 degrees, and theincluded angle from the grating direction of the third kind of thediffraction grating of the diffractive optical element to the aligningdirection of the top layer alignment film is 0±15 degrees. In anotherembodiment, as the included angle between the tilt directions of the toplayer and the bottom layer liquid crystal molecules is 90 degrees, theincluded angle from the grating direction of the first kind of thediffraction grating of the diffractive optical element to the aligningdirection of the top layer alignment film is 30±10 degrees, the includedangle from the grating direction of the second kind of the diffractiongrating of the diffractive optical element to the aligning direction ofthe top layer alignment film is −15±10 degrees, and the included anglefrom the grating direction of the third kind of the diffraction gratingof the diffractive optical element to the aligning direction of the toplayer alignment film is 75±10 degrees. In one embodiment, the includedangle from the grating direction of the first kind of the diffractiongrating of the diffractive optical element to the aligning direction ofthe top layer alignment film is 45±20 degrees, the included angle fromthe grating direction of the second kind of the diffraction grating ofthe diffractive optical element to the aligning direction of the toplayer alignment film is 0±20 degrees, and the included angle from thegrating direction of the third kind of the diffraction grating of thediffractive optical element to the aligning direction of the top layeralignment film is 90±20 degrees.

In some embodiments, the diffractive optical element is designedaccording to the arrangement of the polarizer.

Referring to FIG. 36, for example, the azimuth angle ψ1 of thepolarizing direction 445 of the polarizer, such as the polarizer 425 inFIG. 33, on the light emitting side is 135 degrees, that is the azimuthangle of the transmission axis of the polarizer 425 is 135 degrees, orthe azimuth angle of the absorption axis of the polarizer 425 is 45degrees. The azimuth angle ψ2 of the polarizing direction 455 of thepolarizer, such as the polarizer 415 in FIG. 33, adjacent to thebacklight module is 45 degrees, that is the azimuth angle of thetransmission axis of the polarizer is 45 degrees, or the azimuth angleof the absorption axis is 135 degrees. The diffractive optical element462, similar to the diffractive optical element 32 in FIG. 2, has thegrating region 473 and the grating region 483, respectively having thediffraction grating 474 having the grating direction having the azimuthangle of 0 degree and the diffraction grating 484 having the gratingdirection having the azimuth angle of 90 degrees. The density of thediffraction grating 473 is bigger than or equal to the density of thediffraction grating 483. In this case, the azimuth angle of the longaxis direction of the row constituted by the grating regions 473 and theazimuth angle of the long axis direction of the row constituted by thegrating regions 483 are 0 degree. The azimuth angle of the long axisdirection of the column constituted by the grating regions 473 and thegrating region 483 arranged in alternation is 90 degrees.

The embodiment as shown in FIG. 37 is different from the embodiment asshown in FIG. 36 in that the grating regions 493, similar with thegrating region 473 in FIG. 36, and the grating region 503, similar withthe grating region 483 in FIG. 36 are arranged in alternation. In thiscase, the azimuth angle of the long axis direction 496 of the rowconstituted by the grating regions 493 and the azimuth angle of the longaxis direction 497 of the row constituted by the grating regions 503 are0 degree. The azimuth angle of the long axis direction of the columnconstituted by the grating regions 493 and the grating region 503arranged in alternation is 60 degrees. The embodiment as shown in FIG.38 is different from the embodiment as shown in FIG. 36 in that thegrating regions 513, similar with the grating region 473 in FIG. 36, andthe grating region 523, similar with the grating region 483 in FIG. 36are arranged in alternation. In this case, the azimuth angle of the longaxis direction of the row constituted by the grating regions 513 and thegrating regions 523 arranged in alternation is 0 degree. The azimuthangle of the long axis direction of the column constituted by thegrating regions 513 and the grating regions 523 arranged in alternationis 90 degrees.

Referring to FIG. 39, the azimuth angle ψ3 of the polarizing direction505 of the polarizer, such as the polarizer 425 in FIG. 33, on the lightemitting side is 135 degrees, that is the azimuth angle of thetransmission axis of the polarizer 425 is 135 degrees, or the azimuthangle of the absorption axis of the polarizer 425 is 45 degrees. Theazimuth angle ψ4 of the polarizing direction 515 of the polarizer, suchas the polarizer 415 in FIG. 33, adjacent to the backlight module is 45degrees, that is the azimuth angle of the transmission axis of thepolarizer 455 is 45 degrees, or the azimuth angle of the absorption axisof the polarizer 455 is 135 degrees. The diffractive optical element522, similar with the diffractive optical element 82 in FIG. 4, has thegrating region 533, the grating region 543 and the grating region 553,for example, respectively having the diffraction grating 534 having thegrating direction having the azimuth angle of 135 degrees, thediffraction grating 544 having the grating direction having the azimuthangle of 0 degree, and the diffraction grating 554 having the gratingdirection having the azimuth angle of 45 degrees. In one embodiment,especially for the TN liquid crystal display device, the density of thediffraction grating 544 is gibber than or equal to the density of thediffraction grating 534 and the density of the diffraction grating 554respectively.

Referring to FIG. 40, the azimuth angle ψ5 of the polarizing direction545 of the polarizer, such as the polarizer 425 in FIG. 33, on the lightemitting side is 135 degrees, that is the azimuth angle of thetransmission axis of the polarizer 425 is 135 degrees, or the azimuthangle of the absorption axis of the polarizer 425 is 45 degrees. Theazimuth angle ψ6 of the polarizing direction 555 of the polarizer, suchas the polarizer 415 in FIG. 33, adjacent to the backlight module is 45degrees, that is the azimuth angle of the transmission axis of thepolarizer 455 is 45 degrees, or the azimuth angle of the absorption axisof the polarizer 455 is 135 degrees. The diffractive optical element562, similar with the diffractive optical element 182 in FIG. 8, has thegrating region 573 and the grating region 583, respectively having thediffraction grating 574 having the grating direction having the azimuthangle of 135 degrees and the diffraction grating 584 having the gratingdirection having the azimuth angle of 45 degrees.

Referring to FIG. 41, the azimuth angle ψ7 of the polarizing direction605 of the polarizer, such as the polarizer 425 in FIG. 33, on the lightemitting side is 135 degrees. The azimuth angle ψ8 of the polarizingdirection 615 of the polarizer, such as the polarizer 415 in FIG. 33,adjacent to the backlight module is 45 degrees. The diffractive opticalelement 622 for using is similar with the diffractive optical element292 in FIG. 28, and has the grating region 603 and the grating region613, respectively having the diffraction grating 604 having variousgrating directions and the diffraction grating 614 having the gratingdirection having the azimuth angle of 90 degrees.

In one embodiment, the included angle between the azimuth angles of thegrating direction of the first kind of the diffraction grating of thediffractive optical element and the polarizing direction of thepolarizer on the light emitting side is 135±20 degrees, and the includedangle between the azimuth angles of the grating direction of the secondkind of the diffraction grating of the diffractive optical element andthe polarizing direction of the polarizer on the light emitting side is45±20 degrees. In another embodiment, as the included angle between thepolarizing direction of the polarizer on the light emitting side and thepolarizing direction of the polarizer on the light entering side is 90degrees and the azimuth angle of the polarizing direction of thepolarizer on the light entering side is 135 degrees, the included anglefrom the grating direction of the first kind of the diffraction gratingof the diffractive optical element to the polarizing direction of thepolarizer on the light emitting side is 90±20 degrees, preferably 90±10degrees, and the included angle from the grating direction of the secondkind of the diffraction grating of the diffractive optical element tothe polarizing direction of the polarizer on the light emitting side is0±20 degrees, preferably 0±10 degrees. In another embodiment, as theincluded angle between the polarizing direction of the polarizer on thelight emitting side and the polarizing direction of the polarizer on thelight entering side is 90 degrees and the azimuth angle of thepolarizing direction of the polarizer on the light entering side is 135degrees, the included angle from the grating direction of the first kindof the diffraction grating of the diffractive optical element to thepolarizing direction of the polarizer on the light emitting side is180±20 degrees, preferably 180±10 degrees, and the included angle fromthe grating direction of the second kind of the diffraction grating ofthe diffractive optical element to the polarizing direction of thepolarizer on the light emitting side is 90±20 degrees, preferably 90±10degrees. In one embodiment, the included angle from the gratingdirection of the first kind of the diffraction grating of thediffractive optical element to the polarizing direction of the polarizeron the light emitting side is 45±15 degrees, the included angle from thegrating direction of the second kind of the diffraction grating of thediffractive optical element to the polarizing direction of the polarizeron the light emitting side is 0±15 degrees, and the included angle fromthe grating direction of the third kind of the diffraction grating ofthe diffractive optical element to the polarizing direction of thepolarizer on the light emitting side is 90±15 degrees. In anotherembodiment, the included angle from the grating direction of the firstkind of the diffraction grating of the diffractive optical element tothe polarizing direction of the polarizer on the light emitting side is20±10 degrees, the included angle from the grating direction of thesecond kind of the diffraction grating of the diffractive opticalelement to the polarizing direction of the polarizer on the lightemitting side is 75±10 degrees, and the included angle from the gratingdirection of the third kind of the diffraction grating of thediffractive optical element to the polarizing direction of the polarizeron the light emitting side is 165±10 degrees. In one embodiment, theincluded angle from the grating direction of the first kind of thediffraction grating of the diffractive optical element to the polarizingdirection of the polarizer on the light emitting side is 135±20 degrees,the included angle from the grating direction of the second kind of thediffraction grating of the diffractive optical element to the polarizingdirection of the polarizer on the light emitting side is 90±20 degrees,and the included angle from the grating direction of the third kind ofthe diffraction grating of the diffractive optical element to thepolarizing direction of the polarizer on the light emitting side is180±20 degrees.

In one embodiment, one experiment uses the Konica Minolta CS-2000 tomeasure the N101L6-L07 type liquid crystal display device having thediffractive optical element 212 (T=124 μm, W=117 μm, N=1 μm, M=7 μm) asshown in FIG. 20. The white state and the black state of the liquidcrystal display device are measured for every 5 degrees ofcounter-clockwise rotating of the diffractive optical element 212. Inaddition, the contrast value (white state (255 gray level)brightness/black state (0 gray level) brightness) and the normalizationbrightness of each gray level (brightness of each gray level/white state(255 gray level) brightness) are calculated. Data are shown in table 1.The display device without using the diffractive optical element is onecomparative example. Effect of adjusting the angle of the diffractiongrating for the normalization brightness of the display device for thespecific gray level is shown in table 2. The measuring method for thecharacteristics as shown in table 2 is adjusting the angle of thediffraction grating, and measuring the difference between thenormalization brightness of the display device at the zenith angle of 0°and the brightness of the display device at the zenith angles of 45° or60°, in the specific gray levels (224 gray level, 232 gray level). Eachunit for the gray level reversion is 8 gray levels. The gray levelreversion is happened as the difference between the next one unit of thegray level and the previous one unit of the gray level is negative. Thenormalization difference is the difference between the conditions inwhich the diffraction grating has the azimuth angle of 0 degree and thediffraction grating has the azimuth angle of other rotating angles.

TABLE 1 azimuth angle of diffraction Central grating contrast −85 734−80 761 −75 786 −70 827 −65 864 −60 879 −55 882 −50 873 −45 845 −40 827−35 781 −30 736 −25 687 −20 662 −15 653 −10 653 −5 660 0 681 5 762 10764 15 790 20 809 25 828 30 856 35 865 40 885 45 896 50 905 55 915 60906 65 889 70 857 75 812 80 764 85 734 90 722

TABLE 2 Normalization Normalization brightness brightness graydifference difference azimuth level for between θ of between θ of angleof gray 45° and 0° normalization 60° and 0° normalization diffractionlevel (gray level difference (gray level difference grating reversion224) at θ of 45° 232) at θ of 60° comparative 64~152 56.4% — 58.9% —example  0 non 18.9% 100% 11.8% 100% 10 non 21.9% 116% 16.6% 140% 20 non24.0% 127% 20.0% 169% 30 non 28.8% 153% 25.8% 218% 40 non 35.8% 190%34.5% 292% 45 non 40.3% 214% 39.3% 333% 50 non 43.3% 229% 41.3% 350% 60non 47.3% 251% 44.6% 378%

The side viewing angle can be much improved due to the high density of94%. However, since the single grating direction is used, the result ismuch affected by the rotating angle.

The contrast of the display apparatus is affected by adjusting theincluded angle between the diffraction grating direction and thepolarizing direction of the polarizer.

In another embodiment, one experiment uses the Konica Minolta CS-2000 tomeasure the N101L6-L07 type liquid crystal display device (pixel ofwhich is 800*600,126 PPI and the long side of the pixel of which is203.2 μm, and the short side of the pixel of which is 67.73 μm) havingthe diffractive optical element 462 (S1=9 μm, S2=15 μm, S4=S5=13 μm,D1=D2=1 μm, K1=K2=28 μm) as shown in FIG. 36. Referring to FIG. 2, inother embodiments, the display apparatus (S1=9 μm, S2=15 μm, S3=9 μm,D1=D2=1 μm, S4=S5=41 μm, K1=K2=28 μm) may be used. The white state andthe black state of the liquid crystal display device are measured forevery 5 degrees of counter-clockwise rotating of the diffractive opticalelement 462. In addition, the contrast value (white state (255 graylevel) brightness/black state (0 gray level) brightness) and thenormalization brightness of each gray level (brightness of each graylevel/white state (255 gray level) brightness) are calculated. Theinfluence of the diffraction grating angle to the contrast is shown intable 3 and FIG. 42. The display device without using the diffractiveoptical element is one comparative example. Effect of adjusting theangle of the diffraction grating to the normalization brightness of thedisplay device for the specific gray level is shown in table 4, FIG. 43and FIG. 44.

TABLE 3 azimuth angle of Central diffraction grating 474 contrast −85776 −80 763 −75 777 −70 802 −65 829 −60 863 −55 894 −50 913 −45 923 −40916 −35 898 −30 867 −25 837 −20 814 −15 786 −10 772 −5 757 0 757 5 74310 748 15 767 20 790 25 822 30 844 35 880 40 900 45 916 50 916 55 907 60890 65 853 70 828 75 804 80 786 85 776 90 770

In FIG. 42 and table 3, 0 degree indicates that the azimuth angle of thediffraction grating 474 of the grating region 473 is 0 degree, and theazimuth angle of the diffraction grating 484 of the grating region 483is 90 degrees, as shown in the arrangement condition in FIG. 36. In FIG.42 and table 3, +5 degrees indicates that the azimuth angle of thediffraction grating 474 of the grating region 473 is +5 degree, and theazimuth angle of the diffraction grating 484 of the grating region 483is +95 degrees. The azimuth angle ψ1 of the polarizing direction 445 ofthe polarizer on the light emitting side is fixed at 135 degrees, andthus the included angle from the polarizing direction of the polarizeron the light emitting side to the grating direction of the diffractiongrating 484 is −130 degrees (or +50 degrees) and the included angle fromthe polarizing direction of the polarizer on the light emitting side tothe grating direction of the diffraction grating 474 is −40 degrees (or+140 degrees). The angle of the counter-clockwise direction has apositive value, the angle of the clock-wise direction has a negativevalue, and so forth.

From table 3, it is found, for decreasing the influence to the contrast,the desired condition is that the azimuth angle of the diffractiongrating 474 is about +45 degrees and the azimuth angle of thediffraction grating 484 is 135 degrees. For maintaining the influence tothe contrast lower than 90%, the desired condition is that the azimuthangle of the diffraction grating 474 is 45±20 degrees and the azimuthangle of the diffraction grating 484 is 135±20 degrees. For making theinfluence to the contrast lower than 95%, the desired condition is thatthe azimuth angle of the diffraction grating 474 is 45±10 degrees andthe azimuth angle of the diffraction grating 484 is 135±10 degrees. Asthe included angle between the tilt directions of the top layer liquidcrystal molecule and the bottom layer liquid crystal molecule is 90degrees, the desired condition is that the included angle from thegrating direction of the diffraction grating 474 of the diffractiveoptical element to the tilt direction of the top layer liquid crystalmolecule is 0±20 degrees, preferably 0±10 degrees, and the includedangle from the grating direction of the diffraction grating 484 of thediffractive optical element to the tilt direction of the top layerliquid crystal molecule is −90±20 degrees, preferably −90±10 degrees. Inaddition, included angle from the grating direction of the diffractiongrating 474 to the aligning direction of the first (top layer) alignmentfilm, such as the alignment film 419 in FIG. 34, is 0±10 degrees, andthe included angle from the grating direction of the diffraction grating484 to the aligning direction of the first alignment film is −90±10degrees. As the included angle between the polarizing direction of thepolarizer of the light emitting side and the polarizing direction of thepolarizer of the light entering side is 90 degrees, and the azimuthangle of the polarizing direction of the polarizer of the light emittingside is 135 degrees, the included angle from the grating direction ofthe diffraction grating 474 to the polarizing direction of the polarizerof the light emitting side is 90±10 degrees, and the included angle fromthe grating direction of the diffraction grating 484 to the polarizingdirection of the polarizer of the light emitting side is 0±10 degrees.

From table 3, it is also found, for decreasing the influence to thecontrast, the desired condition is that the azimuth angle of thediffraction grating 474 is about −45 degrees and the azimuth angle ofthe diffraction grating 484 is 45 degrees. For maintaining the influenceto the contrast lower than 90%, the desired condition is that theazimuth angle of the diffraction grating 474 is −45±20 degrees and theazimuth angle of the diffraction grating 484 is 45±20 degrees. Formaking the influence to the contrast lower than 95%, the desiredcondition is that the azimuth angle of the diffraction grating 474 is−45±10 degrees and the azimuth angle of the diffraction grating 484 is45±10 degrees. In this embodiment, the included angle from the gratingdirection of the diffraction grating 474 to the tilt direction of thetop layer liquid crystal molecule, such as the top layer liquid crystalmolecule 428 a in FIG. 34 is 90±10 degrees and the included angle fromthe grating direction of the diffraction grating 484 to the tiltdirection of the top layer liquid crystal molecule is 0±10 degrees. Theincluded angle from the grating direction of the diffraction grating 474to the aligning direction of the top layer alignment film is +90±10degrees, and the included angle from the grating direction of thediffraction grating 484 to the aligning direction of the top layeralignment film is 0±10 degrees. As the included angle between thepolarizing direction of the polarizer of the light emitting side and thepolarizing direction of the polarizer of the light entering side is 90degrees, and the azimuth angle of the polarizing direction of thepolarizer of the light emitting side is 135 degrees, the included anglefrom the polarizing direction of the polarizer of the light emittingside to the grating direction of the diffraction grating 474 is 180±10degrees, and the included angle from the polarizing direction of thepolarizer of the light emitting side to the grating direction of thediffraction grating 484 is 90±10 degrees.

TABLE 4 Normalization Normalization brightness brightness azimuth graydifference difference angle of level for between θ of between θ ofdiffraction gray 45° and normalization 60° and normalization gratinglevel 0° (gray level difference 0° (gray level difference 474 reversion224) at θ of 45° 232) at θ of 60° comparative 64~152 56.4% — 58.9% —example  0 non 41.3% 100.00% 26.8% 100.00% 10 non 42.9% 103.79% 28.5%106.40% 20 non 43.8% 105.98% 31.1% 116.26% 30 non 53.2% 128.77% 49.1%183.48% 40 non 53.2% 128.77% 49.1% 183.48% 45 non 45.1% 109.14% 50.0%186.76% 50 non 44.9% 108.64% 48.7% 182.08% 60 non 42.9% 103.85% 45.3%169.28%

The measuring method for the characteristics as shown in table 4 isadjusting the angle of the diffraction grating, and measuring thedifference between the normalization brightness of the display device atthe zenith angle of 0° and the brightness of the display device at thezenith angles of 45° or 60°, in the specific gray levels (224 graylevel, 232 gray level). Each unit for the gray level reversion is 8 graylevels. The gray level reversion is happened as the difference betweenthe next one unit of the gray level and the previous one unit of thegray level is negative. The normalization difference is the differencebetween the conditions in which the diffraction grating has the azimuthangle of 0 degree and the diffraction grating has the azimuth angle ofother rotating angles.

In comparative example, at an observation angle of (θ,ψ)=(45,270), thedifference value between the normalization brightness at the zenithangle θ=45 and the normalization brightness at the zenith angle θ=0 hasthe maximum value (56.41%) at the 224 gray level. Therefore, theobservation at the zenith angle θ=45 is based on the 224 gray level.With increase of the deviation of the azimuth angle of the diffractiongrating 474 of the diffractive optical element 462 from 0 degreeincreases, the difference value between the normalization brightnessvalues at 224 gray level of θ=45 and θ=0 increases. The difference valuehas the maximum (53.2%) as the deviation reaches about 30˜40 degrees,which is smaller than comparative example (58.9%). The difference valuegets smaller than the maximum value after the deviation of about 40degrees.

In comparative example, at an observation angle of (θ,ψ)=(60,270), thedifference value between the normalization brightness at the zenithangle θ=60 and the normalization brightness at the zenith angle θ=0 hasthe maximum value (58.92%) at the 232 gray level. With increase of thedeviation of the azimuth angle of the diffraction grating 474 of thediffractive optical element 462 from 0 degree increases, the differencevalue between the normalization brightness values at 232 gray level ofθ=60 and θ=0 increases. The difference value has the maximum (50.0%) asthe deviation reaches about 45 degrees, which is smaller thancomparative example (58.9%). By comparing table 2 with table 3, it isfound that the influence from rotating the diffractive optical element462 is smaller than the influence from rotating the diffractive opticalelement 212.

As a whole, even effect of the diffractive optical element 462 deviatedabout 40˜45 degrees is poor, it is still better then that of comparativeexample. Therefore, the diffractive optical element 462 can be used in adeviation range of 0˜60 degrees.

In this embodiment, for improving the gray level reversion, the azimuthangle of the diffraction grating 474 is set at 0±60 degrees, and theazimuth angle of the diffraction grating 484 is set at 90±60 degrees.For further improving the look-down angle characteristic, the azimuthangle of the diffraction grating 474 is set at 0±20 degrees and theazimuth angle of the diffraction grating 484 is set at 90±20 degrees.The included angle from the grating direction of the diffraction grating474 to the polarizing direction of the polarizer of the light emittingside is 135±20 degrees, and the included angle from the gratingdirection of the diffraction grating 484 to the polarizing direction ofthe polarizer of the light emitting side is 45±20 degrees. The includedangle from the grating direction of the diffraction grating 474 to thetilt direction of the top layer liquid crystal molecule is 45±10degrees, and the included angle from the grating direction of thediffraction grating 484 to the tilt direction of the top layer liquidcrystal molecule is −45±10 degrees. The included angle from the gratingdirection of the diffraction grating 474 to the aligning direction ofthe top layer alignment film is 45±10 degrees, and the included anglefrom the grating direction of the diffraction grating 484 to thealigning direction of the top layer alignment film is −45±10 degrees.

In yet another embodiment, one experiment uses the Konica MinoltaCS-2000 to measure the N101L6-L07 type liquid crystal display devicehaving the diffractive optical element 522 (S6=1 μm, S7=1 μm, S8=1 μm,D3=D4=D5=1 μm, S9=S10=S11=1 μm, K3=K4=K5=28 μm) as shown in FIG. 39. Thewhite state and the black state of the liquid crystal display device aremeasured for every 5 degrees of counter-clockwise rotating of thediffractive optical element 522. In addition, the contrast value (whitestate (255 gray level) brightness/black state (0 gray level) brightness)and the normalization brightness of each gray level (brightness of eachgray level/white state (255 gray level) brightness) are calculated.Experiment results are shown in FIG. 45 and FIG. 46. In FIG. 45 and FIG.46, 0 degree indicates that the azimuth angle of the diffraction grating534 of the grating region 533 is 135 degrees, the azimuth angle of thediffraction grating 544 of the grating region 543 is 0 degree, and theazimuth angle of the diffraction grating 554 of the grating region 553is 45 degrees. 24.4% of the area of the diffractive optical element 522is occupied by the area of the grating region 533. 24.4% of the area ofthe diffractive optical element 522 is occupied by the area of thegrating region 543. In addition, 24.4% of the area of the diffractiveoptical element 522 is occupied by the area of the grating region 553.+5 degrees indicates that the azimuth angle of the diffraction grating534 of the grating region 533 is 140 degrees, the azimuth angle of thediffraction grating 544 of the grating region 543 is 5 degrees, and theazimuth angle of the diffraction grating 554 of the grating region 553is 50 degrees. The azimuth angle ψ3 of the polarizing direction 505 ofthe polarizer of the light emitting side is fixed at 135, and thus theincluded angle from the grating direction of the diffraction grating 534to the polarizing direction of the polarizer of the light emitting sideis −5 degrees (or +175 degrees), the included angle from the gratingdirection of the diffraction grating 544 to the polarizing direction 505of the polarizer of the light emitting side is −50 degrees (or 130degrees), and the included angle from the grating direction of thediffraction grating 554 to the polarizing direction 505 of the polarizerof the light emitting side is −90 degrees (or +85 degrees). The angle ofthe counter-clockwise direction has a positive value, the angle of theclock-wise direction has a negative value, and so forth. The influenceof the diffraction grating angle to the contrast for the display deviceis shown in table 5, FIG. 45 and FIG. 46. The display device withoutusing the diffractive optical element is one comparative example. Effectof adjusting the angle of the diffraction grating to the normalizationbrightness of the display device for the specific gray level is shown intable 6, FIG. 47 and FIG. 48.

TABLE 5 azimuth angle of diffraction grating 544 Central contrast −85654 −80 651 −75 630 −70 611 −65 594 −60 587 −55 581 −50 582 −45 583 −40584 −35 585 −30 586 −25 582 −20 591 −15 592 −10 602 −5 604 0 612 5 63010 634 15 634 20 633 25 628 30 617 35 613 40 608 45 604 50 596 55 598 60607 65 617 70 624 75 638 80 642 85 645 90 659

Referring to table 5, from experimental results, it is found that theinfluence for the contrast is low as the azimuth angle of thediffraction grating 534 is 45±15 degrees, the azimuth angle of thediffraction grating 544 is 90±15 degrees, and the azimuth angle of thediffraction grating 554 is 135±15 degrees. In this embodiment, as theincluded angle between the polarizing direction 505 of the polarizer ofthe light emitting side and the polarizing direction 515 of thepolarizer of the light entering side is 90 degrees and the azimuth angleψ3 of the polarizing direction 505 of the polarizer of the lightentering side is 135 degrees, the included angle from the polarizingdirection 505 of the polarizer of the light emitting side to the gratingdirection of the diffraction grating 534 is 90±15 degrees, the includedangle from the grating direction of the diffraction grating 544 to thepolarizing direction 505 of the polarizer of the light emitting side is45±15 degrees, and the included angle from the grating direction of thediffraction grating 554 to the polarizing direction 505 of the polarizerof the light emitting side is 0±15 degrees. The included angle from thegrating direction of the diffraction grating 544 to the tilt directionof the top layer liquid crystal molecule is −45±15 degrees, the includedangle from the grating direction of the diffraction grating 554 to thetilt direction of the top layer liquid crystal molecule is −90±15degrees, and the included angle from the grating direction of thediffraction grating 534 to the tilt direction of the top layer liquidcrystal molecule is 0±15 degrees. The included angle from the gratingdirection of the diffraction grating 544 to the aligning direction ofthe top layer alignment film is −45±15 degrees, the included angle fromthe grating direction of the diffraction grating 554 to the aligningdirection of the top layer alignment film is −90±15 degrees, and theincluded angle from the grating direction of the diffraction grating 534to the aligning direction of the top layer alignment film is 0±15degrees.

In one embodiment, the influence for the contrast is low as the azimuthangle of the diffraction grating 534 is −30±10 degrees, the azimuthangle of the diffraction grating 544 is 15±10 degrees, and the azimuthangle of the diffraction grating 554 is 60±10 degrees. As the includedangle between the polarizing direction 505 of the polarizer of the lightemitting side and the polarizing direction 515 of the polarizer of thelight entering side is 90 degrees and the azimuth angle ψ3 of thepolarizing direction 505 of the polarizer of the light entering side is135 degrees, the included angle from the grating direction of thediffraction grating 534 to the polarizing direction 505 of the polarizerof the light emitting side is 165±10 degrees, the included angle fromthe grating direction of the diffraction grating 544 to the polarizingdirection 505 of the polarizer of the light emitting side is 120±10degrees, and the included angle from the grating direction of thediffraction grating 554 to the polarizing direction 505 of the polarizerof the light emitting side is 75±10 degrees. The included angle from thegrating direction of the diffraction grating 544 to the tilt directionof the top layer liquid crystal molecule is 30±10 degrees, the includedangle from the grating direction of the diffraction grating 554 to thetilt direction of the top layer liquid crystal molecule is −15±10degrees, and the included angle from the grating direction of thediffraction grating 534 to the tilt direction of the top layer liquidcrystal molecule is 75±10 degrees. The included angle from the gratingdirection of the diffraction grating 544 to the aligning direction ofthe top layer alignment film is 30±10 degrees, the included angle fromthe grating direction of the diffraction grating 554 to the aligningdirection of the top layer alignment film is −15±10 degrees, and theincluded angle from the grating direction of the diffraction grating 534to the aligning direction of the top layer alignment film is 75±10degrees.

TABLE 6 Normalization Normalization brightness brightness azimuth θ =difference difference angle of 45° range between θ of between θdiffraction for gray 45° and normalization of 60° and normalizationgrating level 0° (gray level difference 0° (gray difference 544reversion 224) at θ of 45° level 232) at θ of 60° comparative 64~152 56.4% —  58.9% — example  0 Non 37.68% 100.00% 31.49% 100.00% 10 Non35.98% 95.50% 29.46% 93.57% 20 Non 37.44% 99.36% 33.52% 106.47% 30 Non40.10% 106.43% 32.97% 104.69% 40 Non 41.50% 110.13% 34.47% 109.47% 45Non 43.46% 115.34% 34.69% 100.65% 50 Non 41.85% 111.08% 39.71% 126.11%60 Non 43.58% 115.68% 36.88% 117.12%

Referring to table 6, in comparative example, at an observation angle of(θ,ψ)=(45,270), the difference value between the normalizationbrightness at the zenith angle θ=45 and the normalization brightness atthe zenith angle θ=0 has the maximum value (56.41%) at the 224 graylevel. Therefore, the observation at the zenith angle θ=45 is based onthe 224 gray level. With increase of the deviation of the azimuth angleof the diffraction grating 544 of the diffractive optical element 522from 0 degree increases, the difference value between the normalizationbrightness values at 224 gray level of θ=45 and θ=0 increases. Thedifference value has the maximum (43.58%) as the deviation reaches about60 degrees, which is smaller than comparative example (56.4%). Bycomparing table 6 with table 1, it is found that the influence fromrotating the diffractive optical element 522 is smaller than theinfluence from rotating the diffractive optical element 212.

In comparative example, at an observation angle of (θ,ψ)=(60,270), thedifference value between the normalization brightness at the zenithangle θ=60 and the normalization brightness at the zenith angle θ=0 hasthe maximum value (58.92%) at the 232 gray level. At the observationangle of (θ,ψ)=(60,270), with increase of the deviation of the azimuthangle of the diffraction grating 544 of the diffractive optical element522 from 0 degree increases, the difference value between thenormalization brightness values at 232 gray level of θ=60 and θ=0increases. The difference value has the maximum (39.71%) as thedeviation reaches about 50 degrees, which is smaller than comparativeexample (58.9%). The difference value gets smaller than the maximumvalue after the deviation of about 50 degrees.

As a whole, even effect of the diffractive optical element 522 deviatedabout 60 degrees is poor, it is still better then that of comparativeexample. Therefore, the diffractive optical element 522 can be used in adeviation range of 0˜60 degrees. In this embodiment, for improving thegray level reversion, the azimuth angle of the diffraction grating 534is set at 135±40 degrees, the azimuth angle of the diffraction grating544 is set at 0±40 degrees, and the azimuth angle of the diffractiongrating 554 is set at 45±40 degrees. For further improving the look-downangle characteristic, the azimuth angle of the diffraction grating 534is set at 135±20 degrees, the azimuth angle of the diffraction grating544 is set at 0±20 degrees, and the azimuth angle of the diffractiongrating 554 is set at 45±20 degrees. The included angle from the gratingdirection of the diffraction grating 534 to the polarizing direction ofthe polarizer of the light emitting side is 180±20 degrees, the includedangle from the grating direction of the diffraction grating 544 to thepolarizing direction of the polarizer of the light emitting side is135±20 degrees, and the included angle from the grating direction of thediffraction grating 554 to the polarizing direction of the polarizer ofthe light emitting side is 90±20 degrees. In this embodiment, theincluded angle from the grating direction of the diffraction grating 544to the tilt direction of the top layer liquid crystal molecule (such asthe liquid crystal molecule 428 a in FIG. 34) is 45±20 degrees, theincluded angle from the grating direction of the diffraction grating 554to the tilt direction of the top layer liquid crystal molecule is 0±20degrees, and the included angle from the grating direction of thediffraction grating 534 to the tilt direction of the top layer liquidcrystal molecule is 90±20 degrees. The included angle from the gratingdirection of the diffraction grating 544 to the aligning direction ofthe top layer alignment film is 45±20 degrees, the included angle fromthe grating direction of the diffraction grating 554 to the aligningdirection of the top layer alignment film is 0±20 degrees, and theincluded angle from the grating direction of the diffraction grating 534to the aligning direction of the top layer alignment film is 90±20degrees.

In some embodiments, the diffractive optical element is designedaccording to condition of the display device.

Referring to FIG. 49, the display device has a pixel 630. The pixel 630comprises a pixel unit region 637, a pixel unit region 638 and a pixelunit region 639. For example, each of the pixel unit region 637, thepixel unit region 638 and the pixel unit region 639 has a long pixelside 647 and a short pixel side 648 adjacent to each other. The pixelunit region 637, the pixel unit region 638 and the pixel unit region 639may be a red pixel unit region, a green pixel unit region, and a bluepixel unit region, respectively. In other embodiments, the pixel unitregion may be not limited to three regions, and may be constituted byvarious colors. Generally, the length J of the short pixel side 648 isone-third as big as the length L of the long pixel side 647. In someembodiments, the pixel 630 may be for the single color for forming ablack-and-white display device, and in this case, each of the pixel unitregions may have the pixel sides having equal lengths (not shown).

Referring to FIG. 49, in this embodiment, the long axis direction of therow constituted by the grating regions 653 and the long axis directionof the row constituted by the grating regions 663 are both substantiallyparallel to the direction of the short pixel side 648. The long axisdirection of the column constituted by the grating regions 653 and thegrating regions 663 arranged in alternation is substantially parallel tothe direction of the long pixel side 647. In addition, in the rowconstituted by the grating regions 653, the period Px between thegrating region 653 is smaller than or equal to the length J of the shortpixel side 648. In the row constituted by the grating regions 663, theperiod Gx of the grating regions 663 is also smaller than or equal tothe length J of the short pixel side 648. Therefore, light for each ofthe pixel can get effect from at least one grating region 653 and atleast one grating region 663. In some embodiments, in condition offixing the grating structure unit and the grating density in thespecific single pixel unit, the period Px of the grating region 653 orthe period Gx of the grating region 663 is not necessary to be smallerthan or equal to the length J of the short pixel side 648, and thus canbe bigger than the length J. For example, in the display device havingthe red, green and blue pixel unit regions arranged along the shortpixel side cyclically, for the red pixel unit regions, the red pixels inone column have gratings, and the left (right) most next red pixels incolumn have no gratings or have gratings of other kinds of arrangement.

Referring to FIG. 49, in some embodiments, in the column constituted bythe grating regions 653 and the grating regions 663, the period Py ofthe grating regions 653 is smaller than or equal to the length L of thelong pixel side 647. In the column constituted by the grating regions663, the period Gy of the grating regions 663 is also smaller than orequal to the length L of the long pixel side 647. Therefore, light foreach of the pixel can get effect from at least one grating region 653and at least one grating region 663. In some embodiments, in conditionof fixing the grating structure unit and the grating density in thespecific single pixel unit, the period Py of the grating region 653 orthe period Gy of the grating region 663 is not necessary to be smallerthan or equal to the length L of the short pixel side 647, and thus canbe bigger than the length L. For example, along the long pixel side, onerow has gratings, and the left (right) most next row has no gratings orhave gratings of other kinds of arrangement.

The embodiment shown in FIG. 50 is different from the embodiment shownin FIG. 49 in that the long axis of the line constituted by the gratingregions 673 and the grating regions 683 is not parallel to the shortpixel side 668 and the long pixel side 667. In embodiments, the includedangle g between the long axis of the line constituted by the gratingregions 673 and the grating regions 683 arranged in alternation and theshort pixel side 668 is bigger than 0 degree and smaller than 90degrees. In addition, the grating axes of the grating region 673 and thegrating region 683 follow the included angle g. In the period of theline constituted by the grating regions 673 and the grating regions 683arranged in alternation, the period F between the grating region 673 andthe grating region 683 is smaller than or equal to J/cos(g). J indicatesthe length of the short pixel side 668. The long axis of the lineconstituted by the grating regions 673 and the short pixel side 668 hasthe included angle 90-g therebetween. The long axis of the lineconstituted by the grating regions 683 and the short pixel side 668 hasthe included angle 90-g therebetween. In the line constituted by thegrating regions 673 and the line constituted by the grating regions 683,the period V between the grating regions 673 and the period Y betweenthe grating regions 683 are respectively smaller than or equal toJ/cos(90-g). This structure arrangement can be used for resolving moiréissue, or adjusting the main diffraction direction of the diffractiveelement relative to the direction of the display device without changingthe exiting whole arrangement.

Referring to FIG. 50, the compensate direction shifts by the angle g asthe grating axes of the grating region 673 and the grating region 683 isshifted by the angle g with the whole arrangement. In this case, formaintaining the main diffraction direction as not rotating the angle g,the grating region 673 and the grating region 683 may be made withoutchanging the grating axis directions of which as shown in FIG. 51.

The arrangement of the grating region can be adjusted according toactual demands. Referring to FIG. 52 and FIG. 53, for example, thegrating region is arranged according to the corresponding pixel unitregion. For example, the grating regions in the pixel unit region of thesame color or the same structure, such as the single unit having threered, green and blue pixels or the single unit having multiple red, greenand blue pixels, have the same arrangement method. Optionally, thegrating regions in the pixel unit region of different colors ordifferent structures, such as the single unit having three red, greenand blue pixels or the single unit having multiple red, green and bluepixels, have different arrangement methods. For example, for the frontview, the chromatic color of the white gray level is blue. Forcompensating chromatic difference of the white gray level from the frontview (observation angle of θ=0) of the display device, the gratingdensity in the blue pixel unit region may be higher than the gratingdensity in the red and green pixel unit region. In one embodiment asshown in FIG. 54, the pixel unit regions of the same color is designedto have the lines constituted by the same grating region. In addition,the location of the lines arranged in the pixels may be changed. Assuch, the optical moiré issue that would happen easily in the grating ofthe period structure can be avoided. In FIG. 55, the included anglebetween the line constituted by the grating regions and the pixel sidemay be adjusted properly, such as the same included angle g1 in thisembodiment. Referring to FIG. 56, in this embodiment, the linesconstituted by the grating regions corresponding to the upper pixels andthe pixel side have the same included angle g2 therebetween. The linesconstituted by the grating regions corresponding to the lower upperpixels and the pixel side have various included angles g3, g4, g5, g6therebetween. Every pixel has the grating regions of substantially thesame area by the method. Referring to FIG. 57, the lines constituted bythe grating regions and the pixel side may have different includedangles therebetween. Referring to FIG. 58, in this embodiment, the linesconstituted by the grating regions corresponding to the upper pixels andthe pixel side have the same included angle g8 therebetween. The linesconstituted by the grating regions corresponding to the lower pixels andthe pixel side have the same included angle g9 therebetween. Theincluded angle g8 and the included angle g9 are respectively smallerthan or bigger than 90 degrees. The embodiment shown in FIG. 59 may be avariation of the embodiment shown in FIG. 54. The embodiment shown inFIG. 59 is different from the embodiment shown in FIG. 54 in that, inFIG. 59, some grating regions are deviated from the long axis of theline. The deviation degree is limited to a range in the period betweenthe lines, so that the pixels of the same characteristic, such as thesame color or the same LC mode, etc. respectively have the gratingregion of the same area equally. The RGB pixel of each group has thegrating arrangement of the grating regions having the periods Λ1, . . .Λn therebetween. In some embodiments, the RGB pixels of different groupsadjacent to each other may be designed to have different gratingarrangements. The design can be adjusted as long as the period betweenthe RGB pixels and the cycle structure of the grating can bereconstituted.

The line constituted by the grating regions and the pixel side may bedesigned to have different included angles therebetween for decreasingthe moiré issue.

In embodiments, one experiment uses the Konica Minolta CS-2000 tomeasure the N101L6-L07 type liquid crystal display device having thediffractive optical element 462 (S1=9 μm, S2=15 μm, S3=9 μm, D1=D2=1 μm,K1=K2=28 μm, referring to FIG. 2) as shown in FIG. 36. The white stateand the black state of the 8″TN panel are measured. In addition, thecontrast values of the 8″TN panel are calculated. In this embodiment,the condition of fixing S5=13 μm and adjusting the period between thegrating regions, such as the gap distance=20 (S4=−8), 23 (S4=−5), 26(S4=−2), 29 (S4=1), 32 (S4=4), 35 (S4=7), 38 (S4=10), 41 (S4=13), 44 μm(S4=16), between the centers of the circles is used. The experimentresults are shown in table 7.

TABLE 7 Period Area Area of of white black of fist second grating statestate contrast grating grating 20 126 0.24 533 38.5% 18.8% 23 111 0.24455 33.5% 18.8% 26 116 0.25 475 29.6% 18.8% 29 138 0.23 592 26.5% 18.8%32 146 0.23 632 24.1% 18.8% 35 172 0.22 785 22.0% 18.8% 38 165 0.22 74220.3% 18.8% 41 184 0.22 843 18.8% 18.8% 44 202 0.21 975 17.5% 18.8%

The ratio of the area of the grating region to the area of thediffractive optical element can be obtained by calculating. For example,in one embodiment, it is found that as the gap distance between thegrating regions is 26 μm-41 μm, the contrast (equal to the brightness inthe white state/the brightness in the black state) or the brightness inthe white state of the display apparatus (comprising the TN type liquidcrystal display device) would change with the change of the gap distancebetween the grating regions with a linear relation roughly, as shown inFIG. 60. In the condition of S5+K2=S4+K1=41 μm, since the diffractionefficiency shows a substantial symmetrical result and thus can be usedas a standard, the structure variation can be supposed correspondinglyfor increasing or decreasing the diffraction efficiency roughly. Fromthe result shown in FIG. 60, it is obtained from calculations that asthe gap distance between the grating regions (having the structure asshown in FIG. 2 is changed by 1 μm, the diffraction efficiency of thedisplay apparatus would change by about 2.33%, that is, thenormalization brightness would change by 2.3%. Therefore, forincreasing/decreasing the whole oblique diffraction effect, the gapdistance between the grating regions can be increase or decreased from41 μm linearly. Similarly, the contrast may be driven out from thesimilar method. For example, for increasing the whole obliquediffraction effect (or decreasing the normalization brightness) by 10%,the gap distance between the grating regions should be creased from 41μm by 2.1 μm. For example, for increasing the oblique diffraction by10%, the gap distance between the grating regions should be 38.9 μm. Forincreasing the oblique diffraction by 20%, the gap distance between thegrating regions should be 36.7 μm, and so forth. On the contrary, forincreasing the normalization brightness (or decreasing the obliquediffraction effect) by 10%, the gap distance between the grating regionsshould be increased by 2.1 μm from 41 μm. For example, for increasingthe normalization brightness by 10%, the gap distance between thegrating regions should be 43.1 μm. For increasing the normalizationbrightness by 20%, the gap distance between the grating regions shouldbe 45.3 μm, and so forth.

While the disclosure has been described by way of example and in termsof the exemplary embodiment(s), it is to be understood that thedisclosure is not limited thereto. On the contrary, it is intended tocover various modifications and similar arrangements and procedures, andthe scope of the appended claims therefore should be accorded thebroadest interpretation so as to encompass all such modifications andsimilar arrangements and procedures.

1. A display apparatus, comprising: a liquid crystal display devicecomprising: a backlight module; and a liquid crystal panel comprising afirst substrate, a second substrate and a liquid crystal layer, whereinthe liquid crystal layer is disposed between the first substrate and thesecond substrate; a first polarizer disposed on the first substrate; asecond polarizer disposed between the second substrate and the backlightmodule, wherein polarizing directions of the first polarizer and thesecond polarizer have different azimuth angles; and a diffractiveoptical element disposed on a light emitting side of the first polarizerand having a first diffraction grating and a second diffraction grating,wherein grating directions of the first diffraction grating and thesecond diffraction grating have different azimuth angles.
 2. The displayapparatus according to claim 1, wherein an included angle from thegrating direction of the first diffraction grating to the polarizingdirection of the first polarizer is 135±20 degrees, an included anglefrom the grating direction of the second diffraction grating to thepolarizing direction of the first polarizer is 45±20 degrees.
 3. Thedisplay apparatus according to claim 1, wherein an included angle fromthe grating direction of the first diffraction grating to the polarizingdirection of the first polarizer is 180±20 degrees, an included anglefrom the grating direction of the second diffraction grating to thepolarizing direction of the first polarizer is 90±20 degrees.
 4. Thedisplay apparatus according to claim 1, wherein an included angle fromthe grating direction of the first diffraction grating to the polarizingdirection of the first polarizer is 90±20 degrees, an included anglefrom the grating direction of the second diffraction grating to thepolarizing direction of the first polarizer is 0±20 degrees.
 5. Thedisplay apparatus according to claim 1, wherein the diffractive opticalelement further comprises a third diffraction grating, wherein anazimuth angle of the third diffraction grating is different from theazimuth angles of the first diffraction grating and the seconddiffraction grating.
 6. The display apparatus according to claim 5,wherein an included angle from the grating direction of the firstdiffraction grating to the polarizing direction of the first polarizeris 45±15 degrees, an included angle from the grating direction of thesecond diffraction grating to the polarizing direction of the firstpolarizer is 0±15 degrees, an included angle from the grating directionof the third diffraction grating to the polarizing direction of thefirst polarizer is 90±15 degrees.
 7. The display apparatus according toclaim 5, wherein an included angle from the grating direction of thefirst diffraction grating to the polarizing direction of the firstpolarizer is 120±10 degrees, an included angle from the gratingdirection of the second diffraction grating to the polarizing directionof the first polarizer is 75±10 degrees, an included angle from thegrating direction of the third diffraction grating to the polarizingdirection of the first polarizer is 165±10 degrees.
 8. The displayapparatus according to claim 5, wherein an included angle from thegrating direction of the first diffraction grating to the polarizingdirection of the first polarizer is 135±20 degrees, an included anglefrom the grating direction of the second diffraction grating to thepolarizing direction of the first polarizer is 90±20 degrees, anincluded angle from the grating direction of the third diffractiongrating to the polarizing direction of the first polarizer is 180±20degrees.
 9. The display apparatus according to claim 1, wherein anincluded angle between the polarizing direction of the first polarizerand the polarizing direction of the second polarizer is 90 degrees. 10.The display apparatus according to claim 2, wherein the azimuth angle ofthe polarizing direction of the first polarizer is 135 degrees.
 11. Adisplay apparatus, comprising: a liquid crystal display device fordisplaying an image and comprising: a backlight module; and a liquidcrystal panel disposed on the backlight module and comprising: a firstsubstrate; a first alignment film disposed on the first substrate; asecond substrate; a second alignment film disposed on the secondsubstrate, wherein aligning directions of the first alignment film andthe second alignment film have different azimuth angles; and a liquidcrystal layer disposed between the first alignment film and the secondalignment film; and a diffractive optical element disposed on a lightemitting side of the liquid crystal display device and comprising afirst diffraction grating and a second diffraction grating, wherein anazimuth angle of a grating direction of the first diffraction grating isdifferent from an azimuth angle of a grating direction of the seconddiffraction grating.
 12. The display apparatus according to claim 11,wherein an included angle from the grating direction of the firstdiffraction grating to the aligning direction of the first alignmentfilm is 45±60 degrees, an included angle from the grating direction ofthe second diffraction grating to the aligning direction of the firstalignment film is −45±60 degrees.
 13. The display apparatus according toclaim 11, wherein an included angle from the grating direction of thefirst diffraction grating to the aligning direction of the firstalignment film is 0±20 degrees, an included angle from the gratingdirection of the second diffraction grating to the aligning direction ofthe first alignment film is −90±20 degrees.
 14. The display apparatusaccording to claim 11, wherein an included angle from the gratingdirection of the first diffraction grating to the aligning direction ofthe first alignment film is +90±20 degrees, an included angle from thegrating direction of the second diffraction grating to the aligningdirection of the first alignment film is 0±20 degrees.
 15. The displayapparatus according to claim 11, wherein the diffractive optical elementfurther comprises a third diffraction grating, an azimuth angle of thethird diffraction grating is different from the azimuth angles of thefirst diffraction grating and the second diffraction grating.
 16. Thedisplay apparatus according to claim 15, wherein an included angle fromthe grating direction of the first diffraction grating to the aligningdirection of the first alignment film is −45±15 degrees, an includedangle from the grating direction of the second diffraction grating tothe aligning direction of the first alignment film is −90±15 degrees, anincluded angle from the grating direction of the third diffractiongrating to the aligning direction of the first alignment film is 0±15degrees.
 17. The display apparatus according to claim 15, wherein anincluded angle from the grating direction of the first diffractiongrating to the aligning direction of the first alignment film is 30±10degrees, an included angle from the grating direction of the seconddiffraction grating to the aligning direction of the first alignmentfilm is −15±10 degrees, an included angle from the grating direction ofthe third diffraction grating to the aligning direction of the firstalignment film is 75±10 degrees.
 18. The display apparatus according toclaim 15, wherein an included angle from the grating direction of thefirst diffraction grating to the aligning direction of the firstalignment film is 45±20 degrees, an included angle from the gratingdirection of the second diffraction grating to the aligning direction ofthe first alignment film is 0±20 degrees, an included angle from thegrating direction of the third diffraction grating to the aligningdirection of the first alignment film is 90±20 degrees.
 19. The displayapparatus according to claim 11, wherein an included angle between thealigning direction of the first alignment film and the aligningdirection of the second alignment film is 90 degrees.
 20. A liquidcrystal display device for displaying an image, comprising: a liquidcrystal panel comprising: a first substrate; a second substrate; and aliquid crystal layer disposed between the first substrate and the secondsubstrate, wherein the liquid crystal layer comprises liquid crystalmolecules, at least one of the liquid crystal molecules adjacent to thefirst substrate has a first liquid crystal tilt direction, at least oneof the liquid crystal molecules adjacent to the second substrate has asecond liquid crystal tilt direction, an azimuth angle of the firstliquid crystal tilt direction is different from an azimuth angle of thesecond liquid crystal tilt direction; and a diffractive optical elementdisposed on a light emitting side of the liquid crystal panel andcomprising a first diffraction grating and a second diffraction grating,wherein an azimuth angle of a grating direction of the first diffractiongrating is different from an azimuth angle of a grating direction of thesecond diffraction grating.
 21. The display apparatus according to claim20, wherein an included angle from the grating direction of the firstdiffraction grating to the first liquid crystal tilt direction is 90±20degrees, an included angle from the grating direction of the seconddiffraction grating to the first liquid crystal tilt direction is 0±20degrees.
 22. The display apparatus according to claim 20, wherein anincluded angle from the grating direction of the first diffractiongrating to the first liquid crystal tilt direction is 0±20 degrees, anincluded angle from the grating direction of the second diffractiongrating to the first liquid crystal tilt direction is −90±20 degrees.23. The display apparatus according to claim 20, wherein an includedangle from the grating direction of the first diffraction grating to thefirst liquid crystal tilt direction is 45±60 degrees, an included anglefrom the grating direction of the second diffraction grating to thefirst liquid crystal tilt direction is −45±60 degrees.
 24. The displayapparatus according to claim 20, wherein the diffractive optical elementfurther comprises a third diffraction grating, an azimuth angle of thethird diffraction grating is different from the azimuth angles of thefirst diffraction grating and the second diffraction grating.
 25. Thedisplay apparatus according to claim 24, wherein an included angle fromthe grating direction of the first diffraction grating to the firstliquid crystal tilt direction is 45±20 degrees, an included angle fromthe grating direction of the second diffraction grating to the firstliquid crystal tilt direction is 0±20 degrees, an included angle fromthe grating direction of the third diffraction grating to the firstliquid crystal tilt direction is 90±20 degrees.
 26. The displayapparatus according to claim 24, wherein an included angle from thegrating direction of the first diffraction grating to the first liquidcrystal tilt direction is −45±15 degrees, an included angle from thegrating direction of the second diffraction grating to the first liquidcrystal tilt direction is −90±15 degrees, an included angle from thegrating direction of the third diffraction grating to the first liquidcrystal tilt direction is 0±15 degrees.
 27. The display apparatusaccording to claim 24, wherein an included angle from the gratingdirection of the first diffraction grating to the first liquid crystaltilt direction is 30±10 degrees, an included angle from the gratingdirection of the second diffraction grating to the first liquid crystaltilt direction is −15±10 degrees, an included angle from the gratingdirection of the third diffraction grating to the first liquid crystaltilt direction is 75±10 degrees.
 28. The display apparatus according toclaim 20, wherein an included angle between the first liquid crystaltilt direction and the second liquid crystal tilt direction is 90degrees.
 29. A display apparatus, comprising: a display device fordisplaying an image, wherein the display device comprises pixel unitregions, each of the pixel unit regions has a long pixel side and ashort pixel side adjacent to each other; and a diffractive opticalelement disposed on a light emitting side of the display device andcomprising first grating regions and second grating regions, wherein thefirst grating regions have a first diffraction grating, the secondgrating regions have a second diffraction grating, an azimuth angle ofthe first diffraction grating is different from an azimuth angle of thesecond diffraction grating.
 30. The display apparatus according to claim29, wherein, a long axis direction of a line constituted by the firstgrating regions and a long axis direction of a line constituted by thesecond grating regions are substantially parallel to a direction of theshort pixel side, a long axis direction of a line constituted by thefirst grating regions and the second grating regions arranged inalternation is substantially parallel to a direction of the long pixelside.
 31. The display apparatus according to claim 29, wherein, in aline constituted by the first grating regions, a period of the firstgrating regions is smaller than or equal to a length of the short pixelside, in line constituted by the second grating regions, a period of thesecond grating regions is smaller than or equal to a length of the shortpixel side.
 32. The display apparatus according to claim 29, wherein, ina line constituted by the first grating regions, a period of the firstgrating regions is smaller than or equal to a length of the long pixelside, in a line constituted by the second grating regions, a period ofthe second grating regions is smaller than or equal to a length of thelong pixel side.
 33. The display apparatus according to claim 29,wherein, a long axis of a line constituted by the first grating regionsand the second grating regions arranged in alternation and the shortpixel side have an included angle θ therebetween, wherein the includedangle θ is bigger than 0 degree and smaller than 90 degrees, in the lineconstituted by the first grating regions and the second grating regionsarranged in alternation, a period between the first grating regions andthe second grating regions is equal to or smaller than J/cos(θ), whereinJ is a length of the short pixel side; a long axis of a line constitutedby the first grating regions and a long axis of a line constituted bythe second grating region respectively have included angles 90-θ withthe short pixel side, in the line constituted by the first gratingregions and the line constituted by the second grating region, a periodbetween the first grating regions and the second grating regions isequal to or smaller than J/cos(90-θ).